TOEFL Complete the Words: 50 interactive practice tasks
(2026 format)

Question 1. Mangrove forests. Type the missing letters in each box, then check.

Mangrove forests grow along tropical coastlines where salt water meets the land. Their tangled ro trap sedi and slow incoming wa, prote the shore from ero. The dense roots also pro shelter for young fi and crabs, suppo rich coastal food we. Beca these trees store large amounts of carbon, their loss releases greenhouse gases into the atmosphere.

Question 2. Bee pollination. Type the missing letters in each box, then check.

Bees play an essential role in the reproduction of flowering plants. As a bee coll nectar, gr of pollen st to its bo. When it vis the next flo, some of that po is transf, allo fertilization to oc. This mutual relationship benefits both species, and a decline in bee populations threatens global crop yields.

Question 3. The immune response. Type the missing letters in each box, then check.

The human immune system defends the body against harmful invaders. When bact enter a wo, white blood ce quickly trav to the site. These cells reco the intruder and rele chemicals that trig inflammation. Over sev days, the body prod antibodies that bi to the invaders and neutralize the threat, building lasting immunity.

Question 4. Ocean phytoplankton. Type the missing letters in each box, then check.

Phytoplankton are microscopic organisms that drift near the ocean surface. Using sunl, they conv carbon dioxide and wa into sug through photosynthesis. In the pro, they rele enormous amou of oxygen, produ roughly half of what we brea. They also form the ba of the marine food chain, feeding creatures from tiny shrimp to whales.

Question 5. Animal camouflage. Type the missing letters in each box, then check.

Many animals rely on camouflage to survive in their environment. By matc the colors of their surrou, prey can av being seen by pred. Some species chan their appear with the sea, turning wh in winter sn. Others imit leaves or twigs so convincingly that they become almost invisible to a passing predator.

Question 6. The nitrogen cycle. Type the missing letters in each box, then check.

Nitrogen is essential for plant growth, yet plants cannot use it directly from the air. Special bact in the so conv atmospheric nitr into a us form. Plants abs these compo through their ro and use them to bu proteins. When organisms di, decomposers return the nitrogen to the soil, keeping the cycle in balance.

Question 7. Mammalian hibernation. Type the missing letters in each box, then check.

Some mammals survive harsh winters by entering a deep sleep called hibernation. Before the co arrives, they e heavily to st fat. During hibern, their heart ra slows dramat and their body temper dr. This allows them to cons ener when food is scarce, and they emerge in spring thin but alive.

Question 8. How enzymes work. Type the missing letters in each box, then check.

Enzymes are proteins that speed up chemical reactions inside living cells. Each enz has a uni shape that fi a specific mole. When the two con, the reaction proc far more quic than it would alo. Temperature and acid strongly affe enzyme activity, and extreme conditions can permanently destroy their delicate structure.

Question 9. Lichen symbiosis. Type the missing letters in each box, then check.

A lichen is not a single organism but a partnership between two very different species. A fun provides a protec structure, wh algae inside it prod food through photosyn. This arrange allows lichens to surv in harsh pla where neither partner could li alo. They grow slowly but can endure extreme cold and drought for many years.

Question 10. The water cycle. Type the missing letters in each box, then check.

The water cycle describes how water moves continuously between the earth and the sky. Heat from the s causes water to evap from oce and lakes. The vap ri, co, and conde into clouds. Eventually it fal back as ra or sn, flowing through rivers and returning to the sea to begin the process again.

Question 11. Glacial erosion. Type the missing letters in each box, then check.

Glaciers are slow-moving rivers of ice that reshape the land beneath them. As a glac advan, it dr rocks and debr along its ba. This abras material carv deep valle and smooths the underlying sto. When the ice fin melts, it leaves behind ridges of sediment that record the glacier's ancient path.

Question 12. The rock cycle. Type the missing letters in each box, then check.

Rocks are constantly being created, destroyed, and transformed over vast periods of time. Molten mag co and hard into igneous ro. Wind and water then bre it into small parti that set in layers and comp into sedimentary rock. Deep underground, intense he and press can transform these rocks yet again, completing the endless cycle.

Question 13. Earthquakes and faults. Type the missing letters in each box, then check.

Earthquakes occur when stress builds up along cracks in the earth's crust. These cra, called fau, form where massive ro plates me. As the plates pu against each ot, pressure grad accumu. When the rock fin sli, energy is released as seismic waves that shake the ground, sometimes causing enormous damage far from the source.

Question 14. Ocean currents and climate. Type the missing letters in each box, then check.

Ocean currents act like giant conveyor belts that move heat around the planet. Warm wat flo away from the equ toward the po. As it coo, it beco denser and sin, retur along the ocean flo. This circul regulates regional temperatures, and even small changes can dramatically alter weather patterns across entire continents.

Question 15. The carbon cycle. Type the missing letters in each box, then check.

Carbon moves constantly among the atmosphere, living things, and the earth. Plants abs carbon dio from the a during photosynth. Animals e the plants and rele carbon when they brea. When organisms di, their carbon is retur to the so or locked in rock, and burning fossil fuels adds still more to the atmosphere.

Question 16. River deltas. Type the missing letters in each box, then check.

A delta forms where a river meets a larger body of still water. As the flow river slo, it can no longer car its heavy lo of sediment. The parti set and grad bui up into fla, fertile la. Over centuries, these deposits create some of the richest farmland on earth, though they remain vulnerable to flooding.

Question 17. Soil erosion. Type the missing letters in each box, then check.

Soil erosion is the gradual removal of the earth's fertile top layer. Heavy ra and stro wind carry lo soil aw. When farmers remo the natural plant co, the exposed gro ero even fas. Over ti, this process strips the land of nutrients and can turn once-productive fields into barren ground.

Question 18. Sand dunes. Type the missing letters in each box, then check.

Sand dunes are hills of loose sand shaped by the steady action of wind. As wi blo across a desert, it li light gra and pu them forward. The sand piles up ag obstac, grad for a dune. Because the wind never sto, dunes slowly migrate across the landscape, sometimes burying roads and even entire villages.

Question 19. Phases of the moon. Type the missing letters in each box, then check.

The moon appears to change shape over the course of a month. In real, the moon its does not chan; we simply s different amou of its sunlit si. As the moon orb the earth, the ang between the s, earth, and moon shi. This changing angle produces the familiar cycle from a thin crescent to a full moon and back.

Question 20. The life of a star. Type the missing letters in each box, then check.

Stars are born, live for billions of years, and eventually die. A st beg as a vast clo of gas and du. Gra pulls this material toget until the cen grows ho enough for nuclear fus. For most of its li, the star burns steadily, but when its fuel runs out, it collapses or explodes.

Question 21. Tides and gravity. Type the missing letters in each box, then check.

Ocean tides are caused mainly by the gravitational pull of the moon. As the moon pas overhead, its gra tu on the earth's oce. The water bul outward on the si fac the moon, creating a high ti. As the earth rota, each coastline mo through these bulges, so most shores experience two high tides each day.

Question 22. Refraction of light. Type the missing letters in each box, then check.

Light does not always travel in a perfectly straight line. When a ra of light pas from a into wat, it slo down and be. This ben, called refrac, is wh a straw in a gla looks broken. Lenses use the same principle to focus light, allowing eyeglasses and telescopes to sharpen the images we see.

Question 23. Sound waves. Type the missing letters in each box, then check.

Sound is a form of energy that travels through the air as waves. When an object vibr, it pus on the surrou air part. These particles bu into their neigh, passing the ener alo. The vibr eventually rea our ears, where they are converted into signals the brain understands as sound.

Question 24. Magnetism. Type the missing letters in each box, then check.

A magnet is any object that produces a force capable of attracting certain metals. Every mag has t ends, called po. Opposite poles att each ot, wh like poles pu apart. The earth its acts like a giant mag, wh is why a compass needle always points toward the north.

Question 25. Solar energy. Type the missing letters in each box, then check.

Solar panels capture energy from sunlight and turn it into electricity. Each pa conta many small ce made from a special mater. When sunl stri a cell, it kno electrons lo. These moving electrons crea an electric curr that can power homes, and unlike coal, this energy source produces no pollution.

Question 26. The seasons. Type the missing letters in each box, then check.

The changing seasons are caused by the tilt of the earth on its axis. As the earth orb the s, different regi rece varying amounts of dire sunlight. When a hemisph lea toward the s, it experi warm summer da. Half a year later, that same region tilts away and grows cold, giving us winter.

Question 27. The Silk Road. Type the missing letters in each box, then check.

The Silk Road was a vast network of trade routes connecting East and West. Merch carr silk, spi, and precious me across thousands of mi. Along the w, they also excha ideas, relig, and technolo. This exch connected distant civilizations and shaped the cultures of Asia, Europe, and Africa for many centuries.

Question 28. Domesticating animals. Type the missing letters in each box, then check.

Early humans transformed their societies by learning to raise animals. Instead of hun wild herds, people beg to ke them close. They sele the calmest anim and bre them over many genera. Over ti, these creatures prov a steady sup of meat, milk, and labor, allowing communities to grow and settle in one place.

Question 29. The invention of writing. Type the missing letters in each box, then check.

Writing was one of the most important inventions in human history. The earliest scri beg as simple pict pressed into clay tab. Over centur, these sym beca more abstr and eventually repres sounds. Writing allo people to record laws, store knowledge, and communicate across great distances, preserving information far beyond a single lifetime.

Question 30. Roman aqueducts. Type the missing letters in each box, then check.

The Romans built remarkable structures to carry water into their cities. Their aque used a gen downward slo to move water over long distan. Enorm stone arch carried the channels acr valleys. This steady sup of clean wat allowed cit to grow large, feeding public baths, fountains, and homes for hundreds of years.

Question 31. The Renaissance. Type the missing letters in each box, then check.

The Renaissance was a period of extraordinary cultural rebirth in Europe. Beginning in Ita, it rene interest in the a and ideas of anci Greece and Rome. Artists and thin explo new ways of see the wor. This move produ masterpieces of painting, sculpture, and science that continue to influence us today.

Question 32. The spread of paper. Type the missing letters in each box, then check.

Paper was one of the most influential inventions ever to spread across the world. First made in Ch, it was far chea than the mater used bef. As the technol trave westward, it reac the Middle Ea and then Europe. Cheaper wri materials made bo more available, helping knowledge spread to ordinary people.

Question 33. The Bronze Age. Type the missing letters in each box, then check.

The Bronze Age marked a major turning point in the development of early tools. People disco that mel copper with a little t produced a har metal. This new all, called bron, made stro weapons and to. The dem for these metals encour long-distance trade and helped early states grow wealthier and more organized.

Question 34. The magnetic compass. Type the missing letters in each box, then check.

The invention of the compass revolutionized travel across the open sea. Before it exi, sailors rel on the st to find their w. A compass nee always poi toward the nor, even on clou nights. With this reli guide, explorers cou venture far from land and chart entirely new routes across the ocean.

Question 35. The spacing effect. Type the missing letters in each box, then check.

Research on memory has revealed a surprisingly effective way to study. Instead of crammi everything into one long sess, learners remem far more when they spre practice o. Revi material over sev da allows the brain to streng its connections. This tech, known as the spacing effect, produces lasting knowledge rather than information that quickly fades.

Question 36. Classical conditioning. Type the missing letters in each box, then check.

Classical conditioning explains how we learn to associate one thing with another. In a famous experi, a dog lear to conne the sou of a bell with fo. Aft many repeti, the bell alo made the dog saliv. This simple form of lear shows how automatic responses can be trained through repeated pairing.

Question 37. The bystander effect. Type the missing letters in each box, then check.

People are sometimes less likely to help when others are present. This puzz pattern, called the bystander eff, occ because each per assu someone else will a. In a lar crowd, responsib feels sprea thin. Understanding this ten can encourage individuals to step forward instead of waiting for others to respond in an emergency.

Question 38. Working memory. Type the missing letters in each box, then check.

Working memory is the mental workspace where we hold information for a short time. It allo us to keep a phone num in mi just long eno to dial it. This system has a very limi capa, hol only a few ite at on. By grou details into meaningful chunks, however, we can stretch what our memory can manage.

Question 39. Intrinsic motivation. Type the missing letters in each box, then check.

Not all motivation comes from rewards such as money or praise. Someti people work hard simply beca they fi a task interes. This inner dri, called intrinsic motiv, ten to prod deeper enga. Studies sug that offering too many external rewards can actually weaken a person's natural enthusiasm for an activity.

Question 40. Sleep and memory. Type the missing letters in each box, then check.

Sleep does far more than simply rest the tired body. While we sle, the brain rev the events of the d. It streng important memo and disc unnecessary det. This is w students who sle well aft studying often remember more than those who stay awake all night trying to learn.

Question 41. The placebo effect. Type the missing letters in each box, then check.

The placebo effect shows how powerfully the mind can influence the body. When patie beli they are recei real medic, they sometimes fe better. Even a harml sugar pi can red their pain. This surprising respo reve the deep connection between expectation and physical healing, though it does not cure the underlying disease.

Question 42. Language in children. Type the missing letters in each box, then check.

Young children acquire language with remarkable speed and ease. Long before they att scho, they beg to imit the sou around them. Through constant liste and practi, they grad lea the rules of gram. By age five, most children can produce complex sentences without ever having studied a single grammar lesson.

Question 43. Supply and demand. Type the missing letters in each box, then check.

Prices in a market are shaped by the balance between supply and demand. When many people wa a produ that is sca, its pri tends to ri. When shops ha more goo than buyers wa, prices usually fa. This constant adjus helps decide how much of each item is produced and sold across the economy.

Question 44. The division of labor. Type the missing letters in each box, then check.

Dividing work into specialized tasks can greatly increase production. When each work foc on a single st, they beco faster and more ski. Instead of one per buil an entire produ, many hands share the la. This appro, known as the division of labor, allows factories to produce goods at remarkable speed.

Question 45. The growth of the internet. Type the missing letters in each box, then check.

The internet has transformed how people communicate and share information. In its early da, only a f computers were connec toget. As the netw gr, it lin millions of machines around the wor. Today, this global sys allo people to exchange messages, ideas, and services almost instantly across enormous distances.

Question 46. Comparative advantage. Type the missing letters in each box, then check.

Countries often benefit by trading rather than producing everything themselves. Each nat ten to speci in goods it can ma most efficie. It then tra for produ that would be cos to prod at home. This exch allows both partners to enjoy more goods than they could produce on their own.

Question 47. Green space in cities. Type the missing letters in each box, then check.

Parks and gardens provide vital benefits in crowded urban areas. Tr and pla coo the surrou air and cle it of pollution. Green spa also giv residents a pla to rel and exerc. Studies show that access to nature improves both physical health and mental well-being for people living in dense cities.

Question 48. The circular economy. Type the missing letters in each box, then check.

A circular economy aims to reduce waste by keeping materials in use. Instead of throwi products aw, they are repa, reu, or recyc. Manufacturers des goods so their pa can be recov lat. This appro conserves valuable resources and greatly reduces the pollution created by constantly making new things from scratch.

Question 49. How machine learning works. Type the missing letters in each box, then check.

Machine learning allows computers to improve at a task through experience. Rather than follo fixed ru, a program stud large amou of da. It sear for patte and grad adju its predictions. The more exam it receives, the more accurate it becomes, which is how systems learn to recognize speech or images.

Question 50. Automation and work. Type the missing letters in each box, then check.

Automation is changing the kinds of jobs available in modern economies. Machines can now perf many repeti tasks fas than peo. This shi elimin some jo while crea others that requ new skills. As a res, workers increasingly need training to adapt to an economy shaped by rapidly advancing technology.