天然气是一种混合气体，其主要成分是（）。
A.甲烷
B.乙烷
C.丙烷
D.乙烯
参考答案：A
---When are you going to travel to Beijing?
---The train ______ at six tomorrow morning, and I _______ for the station at four o’clock.
A．leaves, leaves
B．is going to leave, am going to leave
C．is going to leave, leaves
D．leaves, am going to leave
工单中的多设备被打√说明（）
A.是多设备工单
B.是单设备工单
C.公用设备工单
