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题库 / Prep2007E1-SC-130
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.
while at the same time they have introduced some 100,000 dangerous chemical pollutants, having
while at the same time introducing some 100,000 dangerous chemical pollutants that have
while they have introduced some 100,000 dangerous chemical pollutants at the same time, and have
but introducing some 100,000 dangerous chemical pollutants at the same time that have
but at the same time introduce some 100,000 dangerous chemical pollutants, having
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but前后需要平行，while引导从句，当从句主语和主句主语相同时，从句的主语和助动词可以省略；
根据语义判断gone virtually unregulated是修饰pollutants的；
A having gone修饰不合理；
B 正确
C they存在指代歧义，指代methods,根据语义判断主语应该是industrialization and methods
D but前后不平行
E but前后不平行
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