题目

Which of the following sentences is RIGHT?  A. Not until his son came back did he go to bed.      B. Not until his son came back he went to bed.  C. Not until did his son come back he went to bed.    D. Not until did his son come back did he go to bed. 答案：A（本题满分7分）如图，斜坡AC的坡度（坡比）为1:，AC＝10米．坡顶有一旗杆BC，旗杆顶端B点与A点有一条彩带AB相连，AB＝14米．试求旗杆BC的高度．