管道系统安装完成后应进行吹扫的工作,吹扫的介质可以是()。
A、空气
B、蒸汽
C、空气和蒸汽
D、惰性气体
参考答案:C
—Mom, where is David?
—He is working _____ that difficult math problem in his room.[ ]
A. for
B. with
C. on
D. in
体积为2米3的物体浸没在水中,求物体受到的浮力大小。