------You are leaving for Beijing Please send me a postcard you are there.------No proble

问题补充：

------You are leaving for Beijing Please send me a postcard you are there.

------No problem.

A. if

B. while

C. although

D. because

答案：

A. if

(答案→)B. while

C. although

D. because

解析：句意：你将要去北京，你在北京期间请邮寄给我一张明信片。分析是你在北京的时候，也就是指在北京期间，故选B