I've got a present from Tom. However really don't know what I should send him_____return.

问题描述:

I've got a present from Tom. However really don't know what I should send him_____return.
A.forB.inC.asD.on
选哪个?为什么?

C IN
IN RETURN有“作为回报”的意思.“我”已从TOM那获得了礼物,所以C符合题意