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完型填空

　　Plants are everywhere．You can find them 　　1　　 all over the world．This is a good thing for us, because if we didn’t have plants, we would not survive(生存)．There would be 　　2　　 life on earth as we know it．　　3　　 are plants so important?There are many reasons, but one of their most important jobs is to 　　4　　 food．Plants provide food for animals and people．

　　But not all plants provide food．Some of them are dangerous to eat．These plants have developed 　　5　　 ways to stop animals or people eating them．One of these ways is to make poison(毒汁)which often 　　6　　 terrible and keeps the animals away．

　　Another way to keep animals away is to grow spikes(尖刺)．The spikes are like sharp needles(锋利的钢针)，and 　　7　　 any animals that comes near．Some plants have stings(刺毛)．When you touch them, your skin turns 　　8　　 or gets hot．Animals soon 　　9　　 not to go near these kinds of plants．But some plants are even better at stopping animals．Usually the animals eat the plants, 　　10　　 these plants catch the animals and eat them!

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阅读理解

　　A prairie is a type of grassland．Prairies are made up of a complete interdependent ecosystem．This means that all kinds of plants and animals in a prairie region depend on one another for survival(生存)．The members of a prairie ecosystem include grasses, flowering plants, animals, soil(土壤), sand, and fire．

　　You may look at a prairie and think there’s nothing there but grass, but that’s not true．Most of the prairie’s living things are below the ground．Underneath the prairie’s surface are roots and bulbs(根茎)．The roots of the prairie flowers and grasses run deep．Some of them are as deep as 3.5 metres below the ground．

　　It is important for the roots to run deep because fires are a part of the prairie ecosystem．When a fire burns through the prairie, plants with shallow(not deep)roots can not survive．Plants that have deep root systems are able to survive the fires．When fire burns across a prairie, it burns dead plants from the top and returns those nutrients(养料)to the soil．This adds to the richness of the prairie soil．Prairies have some of the richest soil in the United States．This cycle of growth and burning has been going on for thousands of years．

　　Big bluestem is the plant that gives parts of the prairie the name“tallgrass prairie”．Big bluestem has very deep roots, and its stems(茎)are often 2 metres tall．

　　The American bison(野牛)or buffalo, is the country’s largest land animal．Its home is on the prairies．In 1830, there were an estimated 30 million to 60 million bison in the United States．By 1889, Americans had made the bison population to fewer than 1,000 animals．Through great efforts, bison are being reintroduced to the prairies．They are also kept in zoos．The bison population has grown to several hundred thousand today．

　　Humans have put the prairie ecosystem in danger．Through constant farming, building, fire prevention, and ignorance(not knowing)of how the prairie works, the United States has lost much of its natural prairie．Through education and other work, we can hope to save some of it．

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