关于加速度，下列说法中正确的是（　　）

A．加速度的方向，总跟速度变化的方向相同

B．物体的速度随着加速度的减小肯定减小

C．只要物体的速度变化大，其加速度必定大

D．物体的速度等于零，其加速度必为零

Lei Feng ____ a lot of things for others in his life, people thanked him for what he _____.[ ]

A. did; had done            

B. had done; had done

C. had done; did                

D. did; did