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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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A：modifier "having……“逻辑上好像是 修饰they的（前置后能明显感觉不妥）。
BUT并列连词（不是绝对要求跟句子，X but Y, 要求Y和X一致） 排除D，while 从属连词 （用法：1.跟-ing participle; 2.修饰adj.和adj. clause）
while ：it's true that the conjunction "while" can be used to signal simultaneity, but it's more often used to signify contrast. 本句while作从属连词表对比。
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