目前使用的三相五孔插座，作用是使N线与PE线分开连接。
参考答案：对
A new bridge ______ across the river and it is expected to open next year.
A．was building
B．is built
C．will build
D．is being built
急性大面积肺血栓栓塞的主要临床表现是（）
A.休克与低血压
B.晕厥
C.咯血
D.咳嗽、咳痰
E.呼吸困难与急促
