在液压实验中对于设计压力大于0.6 MPa的天然气管道，应以( )为介质进行强度和严密性的试验。
A．水B．油C．空气D．天然气
参考答案：A
The old lady ______ the girl ten Yuan for washing windows, most of ______ hadn’t been cleaned for a long time.
A．spent, those
B．paid, that
C．paid, these
D．paid, which
