549.My friend,who ______ on the International Olympic Committee all his life,is retiring next month.
A.served
B.is serving
C.had served
D.has served
550.I won't tell the student the answer to the math problem until he _____ on it for more than an hour.
A.has been working
B.will have worked
C.will have been working
D.had worked
549.答案是D;根据时间状语all his life和is retiring判断，此处应用现在完成时。
550.答案是A;主句为一般将来时态，时间状语从句要用一般现在时或现在完成时。
