题目

But for their help, we_________ the program in time. A. can not finish B. will not finish C. had not finished D. could not have finished 答案：D11．运动员甲将足球以20m/s的速率沿水平直线踢给运动员乙，乙立即以30m/s的速率又将该足球踢给甲，则该足球在这一往返运动过程中平均速率是24m/s，平均速度是0m/s．