气焊时，回火保险器一般装在（）
A、氧气瓶出气口
B、乙炔瓶出气口
C、两种瓶出气口都可以
D、装在焊拒上
参考答案：B
--What time do you usually get up,Rick?
--I usually get up five o'clock. [ ]
A. in
B. at
C. on
D. For
