Question

【题目】Over the past half century, ________ chemical fertilizers has become very common in farming.

A. having usedB. useC. used D. using

Answer 1

【答案】D

【解析】

试题分析：句意：在过去的半个世纪，在农业中使用化肥已经很普遍。此处是作主语，故用动词-ing形式，故选D。