电流在单位时间内做的功叫______．其单位有：______；常用单位有：______．计算电功率公式：______（式中单位P→______；W→______；t→______；U→______；I→______）．利用公式计算时单位要______．计算电功率还可用公式：P=______、P=______、______．

As time went by, the truth had ___.

A．come true

B．come up

C．come to light

D．come forth