More and more scientists are interested in learning about dinosaurs (恐龙). They want to find the reasons __31__ the dinosaurs died out.    Most scientists think that millions of years __32__, dinosaurs could live on the earth happily and safely because the __33__ earth was warm and wet at that time. There were green __34__ everywhere. Dinosaurs could easily find enough __35__. About 95 million years ago, most of the earth became __36__ and dry because a little planet hit __37__ heavily. As a result, almost all the forests __38__. The dinosaurs couldn't find enough food. Most of them __39__.    But some scientists __40__ think so. They think fighting __41__ the animals is the main reason of the dinosaurs' __42__. They think about 95 million years ago, new kinds of animals came to the earth. Most of them had big brains (大脑) and they killed many dinosaurs. Besides, there were __43__ many fights between the dinosaurs. Although these fights happened more than 100 million years ago, __44__ we can tell __45__ the animal's footprints (脚印) that fights did take place.    (    )31. A. when       B. why          C. how         D. where    (    )32. A. in         B. later       C. before         D. ago    (    )33. A. whole       B. all         C. both         D. none    (    )34. A. rivers      B. forests           C. food         D. sunshine    (    )35. A. food to eat    B. room to live   C. air to breath         D. water to drink    (    )36. A. rainy      B. smaller      C. bigger       D. cold    (    )37. A. the dinosaurs   B. the moon     C. the earth      D. the sun    (    )38. A. grew too slowly  B. grew too fast   C. disappeared  D. stopped growing    (    )49. A. moved      B. hid       C. stopped growing   D. died    (    )40. A. not       B. don't       C. aren't       D. won't    (    )41. A. for       B. between     C. in         D. of    (    )42. A. death      B. dead      C. die        D. dying    (    )43. A. also      B. too       C. not         D. no    (    )44. A. but       B. /        C. and        D. so    (    )45. A. on       B. in        C. by         D. with

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