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
Although he had to spend lots of money for going to the ball, he accepted the invitation.____,
the ball was important to him. [ ]
A. After all
B. In all
C. First of all
D. Above all
有一瓶氢氧化钠溶液，平均每1600克水中溶有25克钠离子，这种溶液的百分比浓度是______．
