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题库 / Prep2007E1-SC-97
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, which have
but introducing some 100,000 dangerous chemical pollutants at the same time that have
but at the same time introducing some 100,000 dangerous chemical pollutants, having
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bc怎么选
while at the same time introducing some 100,000 dangerous 同时也做了。。是ing逻辑，与前面的动作发生时一同发生的意思， while doing， at the same time doing
c错在they，后面还有一个they，两个they指代不同的东西
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