三相电动机接在同一电源中，作三角形联接时的总功率是作星形联接时3倍。
参考答案：对
His uncle went abroad in 2010, and _______since．
A．has not been heard of
B．had not been heard of
C．had not heard of
D．has not heard of
黄疸是由于血液中何种物质增多引起的
A．胆红素B．胡萝卜素C．核黄素(维生素B2)D．维生素AE．胆绿素
