— will you come back from Shanghai?—In one month.A. How long B. How oftenC. How soonD. How

问题补充：

— will you come back from Shanghai?—In one month.

A. How long

B. How often

C. How soon

D. How fast

答案：

A. How long

B. How often

(答案→)C. How soon

D. How fast

解析：句意:-你多久才从上海回来？-一个月以后。how long 多长时间，针对一段时间提问；how often 多久一次，提问频率；how soon 多久，多快，经常跟一般将来时连用；how fast 多快，提问速度。根据句意可知，这里问的是多久才能回来，故选C。