—Oh, sorry, what did you say just now?  

—I asked _______.[ ]

A. Where he comes from                  

B. where did he come from

C. where he came from                  

D. when did he go

两台变压器可以并联运行，但条件之一是：并联变压器的( )必须相同。

A．联结组

B．空载电流

C．铜损和铁损

D．容量