结构缝隙中的水银，可以用哪种无损检测方法检测？（）
A、涡流检测法。
B、x射线检测法。
C、渗透检测法。
D、超声波检测法。
参考答案：B
Wang Lei watches TV at home, maybe only once a month. [ ]
A. hardly ever
B. always
C. often
D. never
It was on July 1, 2006 ___ Qinghai-Tibet railway began operation, ____ is a symbolic project in China’s West Development Strategy．
A．when; that
B．that; when
C．which; when
D．that; which
