晶闸管开关电路有（）种类型。
A.1
B.2
C.3
D.4
参考答案：B
It was not until I came here ________I realized this place was famous for not only its beauty but also its weather. (2012·湖南，30)
A．who
B．that
C．where
D．before
吊装作业应采用什么样的索具？
