—May I speak to your manager Mr.Williams at five o’clock tonight?

—I’m sorry. Mr. Williams ________ to a conference long before then.

A．will have gone

B．had gone

C．would have gone

D．has gone

两输入逻辑门，当A、B都为0时，F才为1，是（）

A、或非门

B、与非门

C、或门

D、与门