Question

---______ will Mr．Green be back?

---In a week, I think．

1. A.
   How often
2. B.
   How many
3. C.
   How long
4. D.
   How soon

Answer 1

D
答语中in a week意为“一周之后”，表示将来的一个时间，所以应用how soon来提问，意为“多久以后”。