题目

_____ we were worried about was _______ they could manage to control the pollution. A. That; how   B. That;  whether    C. What;  that   D. What; whether 答案：D一个作匀速直线运动的物体，他在第8s内的速度是8m/s，则它在第4s内的速度是________m/s，它通过40m路程的时间是________s．