【题目】Over the past half century, ________ chemical fertilizers has become very common in farming.
A.having used
B.use
C.used
D.using

【答案】D
【解析】考查动名词。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，故用动名词形式，故选D。