U形液柱压力表是由一“U”字形的（）构成的。
A.透明管
B.金属管
C.玻璃管
D.塑料管
参考答案：C
The life of a professional tennis player is tough ________ you never seem completely free to do _______ you like --- even in the off-season.
A．when; what
B．because; that
C．as; whatever
D．when; whatever
管径小于1000mm的预应力钢筋混凝土管和自应力钢筋混凝土管充满水后经（）ｈ方可进行水压试验。
A、12
B、24
C、48
D、72
