题目内容
根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
Winter begins in the north on December 22nd.People and animals have been doing what they always do to prepare for the colder months, squirrels, for example, have been busy gathering nuts from trees. 1.
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. 2. 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. 3. 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.
4. 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. 5.
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.
