- Will you be available at three o'clock tomorrow afternoon? - No. I a lecture then.A. a

问题补充：

- Will you be available at three oclock tomorrow afternoon?

- No. I a lecture then.

A. are attending

B. will have attended

C. will attend

D. will be attending

答案：

A. are attending

B. will have attended

C. will attend

(答案→)D. will be attending

解析：考查动词时态。题意：“明天下午3点你有空吗？”“没空。我要听一个报告。”答句说的是未来某个时间点正在进行的动作，所以要用将来进行时态。D项正确。