Question

【题目】In my opinion, the key ____air pollution is to inspire people to take public transport in big cities.

A. reduced B. reducing C. to reduce D. to reducing

Answer 1

【答案】D

【解析】

考查固定结构。句意：在我看来，在大城市减少空气污染的关键是鼓励人们乘坐公共交通。the key to doing sth.“做某事的关键”，故选D。