在竖井内(暗装)的水管可采用镀锌铁皮套管，套管的上下口均要高出楼板厚度( )cm。
A．1～2B．2～3C．3～4D．4～5
参考答案：B
33. --- How can you be late for such an important conference?
--- Sorry! But my flight was ______ by fog.
A．taken over
B．held up
C．turned down
D．handed out
