Question

I haven't seen you for a couple of days. What have you been up ________.

1. A.
   in
2. B.
   with
3. C.
   for
4. D.
   to

Answer 1

D
【巧解导析】What's up? 表示“怎么回事？”；What are you up to? 表示“你在干什么？”，句中up是副词，to为介词，后面直接接名词．不能说up to do或up to doing，句中的to也不能改为for，with或其他介词．