问题补充：
-- will the foreign students be back from Nanjing?
--In two days, I think.
A. How soon
B. How often
C. How fast
D. How long
答案：
(答案→)A. How soon
B. How often
C. How fast
D. How long
解析：疑问词辨析. How soon 多久; How often 多久一次;How fast多快;How long多长.
根据答语,两天以后，可知上文对将来时间进行提问，故用how soon来提问。选A.
