信号发出后如有紧急情况，可随时发出（）信号。
A.下放
B.停车
C.提升
参考答案：B
两个不完全相同的梯形一定不能拼成一个平行四边形．______．
All the others seemed to know each other and I began to feel .
A．given away
B．fallen behind
C．turned down
D．left out
