A. To travel as fast as it can. B. To overcome the Earth gravity. C. To get away from the air resistance. D. To have strong power in its operation. 参考答案:B 答案解析:从文章的第一段最后一句“地心引力是火箭飞行中的一个重要因素,如果我们想到达太空或者离开地球,我们就必须脱离地心引力”,可以得出本题的答案应为B。
第8题: [单项选择]肺的募穴为( ) A. 云门 B. 肺俞 C. 中府 D. 尺泽 参考答案:C