—He has never been to Shanghai, _____?   —_______. He has been there twice.

A．has he; No, he hasn’t

B．hasn’t he; No, he hasn’t

C．has he; Yes, he has

D．hasn’t he; Yes, he has

2.5PB20Z表示（）。

A、频率为2.5MHz

B、圆晶片直径为20㎜

C、晶片材料为钛酸钡陶瓷

D、以上都对