电源系统中通常使用什么颜色来分别标识三相电源?()
A.红、黄、绿
B.红、黄、蓝
C.黄、绿、蓝
D.红、黄、黑
参考答案:B
It’s reported that the police will soon ____ the case of two missing children.
A.look into
B.look after
C.look upon
D.look out