Question

- Do you know _______? 

-At 8:00 a.m.

1. A.
   who to talk with
2. B.
   when to have a meeting
3. C.
   what to do next
4. D.
   where to go swimming

Answer 1

B
疑问代词或副词可以和动词不定式连用，充当简单句的某个句子成分。根据答语可知询问的是时间，故用when来引导。