电源的效率定义为外电路电阻消耗的功率与电源的总功率之比。在测电源电动势和内电阻的实验中得到的实验图线如图所示，图中U为路端电压，I为干路电流，a、b为图线上的两点，相应状态下电源的效率分别为、.由图可知、的值分别为(    )

A．、

B．、

C．、

D．、

— How did you find your sister in such a big and strange city?

— I ____ her in the railway station when I was looking for the police for help. [ ]

A. came about

B. came out

C. came up

D. came across