have you been a member of Greener China?For two years.A. How oftenB. How longC. W

问题补充：

--- have you been a member of Greener China?

--- For two years.

A. How often

B. How long

C. When

D. How far

答案：

A. How often

(答案→)B. How long

C. When

D. How far

解析：How often多久一次；How long多长，多久；When什么时候；How far多远；根据下文，两年了。可知上文指的是，你成为绿色中国的一员多久了？故选Ｂ。