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

—“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

请帮忙给出正确答案和分析，谢谢！