have they been married? —For twenty years.A. How farB. How longC. How often D. How soon

问题补充：

have they been married? —For twenty years.

A. How far

B. How long

C. How often

D. How soon

答案：

A. How far

(答案→)B. How long

C. How often

D. How soon

解析：句意：他们结婚多长时间了？二十年了。介词for后跟一段时间，一段时间要用how long提问，故选B。