题目

   Winter begins in the north on December 22nd.People and animals have been doing  what they always do to prepare for the colder months, Sqzeirrels,  for example,  have  been busy gathering nuts from trees.    3 6       They examined differences between red squirrels and gray squirrels in the American  state of Indiana.  The scientists wanted to know how these differences could affect the  growth of black walnut(黑胡桃）trees.37    The black walnut tree is also a central  part of some hardwood forests.       Rob Swihart of Purdue University did the study with Jake Goheen,  a former   Purdue student nowat the University of New Mexico.  The two researchers estimate   that several times as many walnuts grow when gathered by gray squirrels as compared   to red squirrels.Gray squirrels and red squirrels do not store nuts and seeds in the same   way.  Gray squirrels bury nuts one at a time in a number of places.    38    So some nuts   remain in the ground.  Conditions are right for them to develop and grow the following   spring.  Red squirrels, however, store large groups of nuts above ground.        3 9    But Professor Swihart says their numbers began to decrease as more forests   were cut for agriculture.  Red squirrels began to spread through the state during the past   century. The researchers say red squirrels are native to forests that stay green all year,   unlike walnut trees.  They say the cleaning of forest land for agriculture has helped red   squirrels invade（涌入）Indiana.    40       A. Gray squirrels are native to Indiana.     B. But they seldom remember where they buried every nut.     C. Red squirrels bury nuts in a different way.     D. The black walnut is the nut of choice for both kinds of squirrels.     E. Jake Goheen calls them a sign of an environmental problem more than a cause.     F. Scientists are  worried  that they will drive away the gray squirrels.     G. Well, scientists have been  busy gathering information about what the squirrels        do with the food they collect.   答案：GDBAE

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