空气炮主要组成部分有（）等。
A、贮气罐；
B、炮管；
C、炮筒；
D、安全装置。
参考答案：A, B, C
Tom has been here ______ just one year, but his father has worked here ______ ten years ago.[ ]
A. since; for
B. since; since
C. for; since
D. for; /
生铁形成过程主要是（）和其它元素进入过程。
A.还原
B.氧化
C.渗碳
D.渗碳和还原
