—I joined the League May . What about you? —I’ve been a League member three years.A.

问题补充：

—I joined the League May, . What about you?

—I’ve been a League member three years.

A. in; for

B. on; in

C. on; for

D. in; since

答案：

(答案→)A. in; for

B. on; in

C. on; for

D. in; since

解析：句意：我在5月入的团。---我当团员已经三年了。in后面跟时间，时间为年，月。for后跟时间段。on是指具体到某一天，since作介词时，后接表示过去时间点的名词、代词、动名词；作连词时，后接一般过去时的从句；在含有since的句子，谓语动词用现在完成时。at后跟时间点。故而选A.