單項選擇。It'sbadtothrowaboutpapereverywhere.Wemustavoid

問題詳情：

單項選擇。

It's bad to throw about paper everywhere. We must avoid ________ that.

A. do  B. doing     C. did  D. to do

【回答】

B

知識點：動詞和動詞短語

題型：選擇題