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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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AC. 后面they were developed的they指的是pollutants，故前面不能用they来指代industrialization and modern methods（一句话两个they指代不同）
AE. have gone regulated的主语应该为pollutants，若用having，则主语变成了industrialization and modern methods
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