Next fall, when you see geese heading south for the winter, flying along in "V" formation, you might consider what science has d

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问题     Next fall, when you see geese heading south for the winter, flying along in "V" formation, you might consider what science has discovered as to why they fly that way. As each bird flaps its wings, it creates an up-lift for the bird immediately following. By flying in "V" formation, the whole flock adds at least 71 percent greater flying【C1】______than if each bird flew on its own. People who share a common direction and【C2】______of community can get【C3】______they are going more quickly and easily, because they are traveling【C4】______the thrust of one another. When a goose falls out of【C5】______, it suddenly feels the drag and resistance【C6】______trying to go it alone and quickly gets back into the formation to take【C7】______of the lifting power of the bird【C8】______front. If we have as much sense as a goose, we will【C9】______in formation with those people who are【C10】______the same way we are. When the head goose gets tired, it【C11】______back in the wing and another goose flies to the【C12】______. It is【C13】______to take turns doing demanding jobs, whether with people or with geese【C14】______south. Geese honk from behind to encourage those【C15】______front to keep up their speed. Finally, and this is important, when a goose gets sick or is【C16】______by gunshot, and falls out of formation, two other geese fall【C17】______with that goose and follow it down to【C18】______help and protection. They stay with the fallen goose until it is able to fly or【C19】______; and only then do they launch out on their own, or with another formation to catch up with their group. If we have the sense of a goose, we will stand by each other【C20】______that.
【C6】

选项 A、at
B、of
C、off
D、to

答案B

解析
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