电话闭塞法期间，发车信号，应在列车前进方向（）处显示，必须在司机动车或鸣笛回示后方可（）。
参考答案：第二个车门；收回
It is only by practising English for several hours every day _________ be able to use it freely.
A．will you
B．may you
C．that you will
D．when you must
氢损伤
