每个生产矿井必须至少有()个安全出口。
A、1
B、2
C、3
D、4
参考答案:B
–What do you do with the used books?
–We will _________ to the children in the poor areas.
A.give them away
B.take them off
C.pick them up
D.put them out
电流的方向就是导体中电子的运动方向。