There must be a time in every man's life ________.[ ]

A. that he is in low spirits

B. which he is in low spirits

C. when he is in low spirits

D. then he is in low spirits

电缆运行人员应按要求定期到现场使用（）测量金属护层电流。

A.有功功率表；

B.钳形电流表；

C.电度表；

D.电压表。