超声换能器（探头）的作用是（）
A.发射超声波
B.接收超声波
C.发射和接收超声波
D.放大超声波
E.滤过超声波
参考答案：C
三相负载作三角形联结时，若测处三相电流相等，则三个线电流必须相等。
The very biggest and most murderous wars during the industrial age were intra-industrial wars that （） Second Wave nations like Germany and Britain against one another.
A．pitted
B．clipped
C．alleged
D．embarked
