Every minute is made full use of _________ our lessons before the exam.

A．studying

B．studied

C．to study

D．being studied

一个重为20N的物体受到20N的向上拉力时，该物体处于（　　）

A．静止状态

B．匀速上升

C．匀速下降

D．以上三种都有可能