请教prep 1一题

Padmeelena

130. (31416-!-item-!-188;#058&004490)

Industrialization and modern methods of insect control have improved the standard of living around
the globe while at the same time they have introduced some 100,000 dangerous chemical
pollutants, having gone virtually unregulated since they were developed more than 50 years ago.

(A) while at the same time they have introduced some 100,000 dangerous chemical pollutants,
having
(B) while at the same time introducing some 100,000 dangerous chemical pollutants that have
(C) while they have introduced some 100,000 dangerous chemical pollutants at the same time, and
have
(D) but introducing some 100,000 dangerous chemical pollutants at the same time that have
(E) but at the same time introduce some 100,000 dangerous chemical pollutants, having

(A)    整个句子中的两个代的是pollutants；having gone…分词结构有作伴随状语修饰have introduced的歧义，而不是作代词they指代对象不一致，划线部分they没有指代对象，未划线部分的they指
pollutants的定语。
(B)正确
(D) but +    现在分词的用法错

为什么A说划线部分they没有指代对象呢?不是指methods 吗?
(D) but +    现在分词的用法错,错在哪儿呢?
but到底要怎么用呢?
谢谢大家

jasonhaha

D中的BUT后面要跟句子，但是题目里面是短语，你找不出动词的。
个人认为A的THEY没有问题，但是后面状语修饰的主语不明确，可以是METHOLDS，也可以是POLLUTANTS

Padmeelena

谢谢啦