.---- The presidents of China and the USA had ___interview a short time ago.

---- And it was __great success.

A．an; /

B．the; a

C．an; a

D．the; /

同步是指触发电路与主电路在（）上有相互协调、配合的关系

A.电压和电流

B.频率和相位

C.功率和阻抗角

D.频率和电压的比率