144 exercícios originais de gramática em contexto. Cada um traz um texto curto com lacuna, cinco alternativas e a explicação da regra em português.
Coleção autoral — separada do banco de questões de provas do ENEM e vestibulares.
Commercial whaling is no longer the main threat to large whales; shipping is. Collisions with vessels kill an unknown but substantial number every year, and chronic engine noise interferes with the low-frequency calls that whales use to find each other across …
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Lion numbers across Africa have fallen by roughly half in three decades, and the cause is not what films suggest. Trophy hunting attracts most public anger, but the majority of lions are killed by herders protecting cattle, usually with poison, and the rest lo…
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Public libraries survive because they keep redefining what they are for. Circulation of physical books has fallen in most countries, yet visits have not, because the building now provides free internet access, a warm room, help with online benefit applications…
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Traditional hard cheese is a technology for storing summer in a form that survives winter. Milk that would spoil in two days becomes a wheel that keeps for two years, and every step in the process exists to control which microorganisms thrive. ___ by hand twic…
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Water hyacinth is the clearest example of a plant punished for doing exactly what it is good at. Native to the Amazon basin, it absorbs nutrients from water at extraordinary speed, which is why nineteenth-century collectors carried it around the world as an or…
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The grey parrot is among the most intelligent animals ever studied in a laboratory, capable of using words referentially rather than by imitation alone. It is also among the most heavily trafficked. Trappers take chicks from nest holes in trees that took a cen…
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Organic certification is a bureaucratic process rather than a philosophical one. An inspector examines records, soil tests and input receipts, and the land must be free of prohibited substances for a defined conversion period before anything can be labelled. T…
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Dentistry is one of the few areas of medicine where prevention is cheap, effective and still unevenly applied. Water fluoridation at recommended levels reduces decay across an entire population without requiring anybody to change their behaviour, which is prec…
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Tea and coffee are grown by roughly twenty-five million smallholders, most of them farming less than two hectares, and both crops share a structural problem: the value is added after the farm gate. Roasting, blending and branding happen in consuming countries,…
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Neutering is the least glamorous part of animal welfare and probably the most effective. Every unplanned litter competes for the same limited number of homes, and shelters in most large cities are permanently full. For this reason many rescue organisations wil…
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Shelters report the same pattern every January: animals adopted as gifts in December are returned within weeks. The reasons are rarely cruelty; they are arithmetic. A medium-sized dog needs two walks a day for twelve to fifteen years, and veterinary bills for …
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___ that broadcasting income would rise indefinitely, several national federations signed spending commitments in the last decade that they are now unable to meet. Television money has not disappeared, but it has fragmented: audiences moved to streaming platfo…
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Football clubs are unusual businesses: they are judged weekly, their assets can be injured, and their supporters will not accept the argument that a bad season is acceptable if the accounts are healthy. That pressure explains why so many boards choose the tran…
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Giant panda conservation is the most expensive rescue operation ever mounted for a single species, and it divides biologists. Supporters note that protecting panda habitat also protects an entire mountain ecosystem containing thousands of less charismatic spec…
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Between 1950 and 1970 dozens of cities in Europe and the Americas dismantled their tram networks. The reasoning seemed sound at the time: rails were expensive to maintain, buses were flexible, and the private car was the future. Planners now wish they ___ thos…
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Algorithms now make decisions that used to belong to people: who is offered credit, whose CV reaches a human recruiter, which neighbourhoods receive extra policing. The difficulty is that a model trained on historical data inherits whatever bias the history co…
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Tropical forest is not a single thing. From the air it looks uniform, but ecologists distinguish primary forest, which has never been cleared, from secondary growth that returns after logging and holds a fraction of the original diversity. The economics are br…
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Helicopter maintenance is governed by rules written after accidents. Unlike a fixed-wing aircraft, a helicopter depends on a single rotor system in which the failure of one component is rarely survivable, so airworthiness authorities require operators to ___ a…
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The recovery of several crocodilian species is one of the least celebrated successes in conservation. In the 1970s the spectacled caiman of the Pantanal was being slaughtered on an industrial scale for the leather trade, and the American alligator was formally…
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The Moon keeps one face permanently turned towards us, a consequence of tidal forces that slowed its rotation until it matched its orbit. The far side was therefore a complete mystery until a Soviet probe photographed it in 1959, and the images revealed a surf…
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White-nose syndrome has killed millions of hibernating bats in North America since the fungus arrived from Europe, probably on the boots of a caver. The disease wakes the animals repeatedly during winter, forcing them to burn fat reserves at a season when ther…
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Bottlenose dolphins in Laguna, in southern Brazil, have cooperated with local fishermen for generations, driving mullet towards the nets and signalling the moment to cast with a distinctive dive. The behaviour is learned, not instinctive, and it passes from mo…
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The modern zoo is an uncomfortable institution. Its critics point out that enclosures rarely reproduce the space or complexity of a wild territory, and that a large predator pacing behind glass teaches visitors very little about ecology. Its defenders answer w…
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___ for centuries as symbols of treachery, snakes are only now being reassessed by conservation biologists. Field studies in southern Brazil suggest that a single rattlesnake may remove several hundred crop-eating rodents from a farm each season, work that wou…
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