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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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有人问了这个问题，这是RON的回答："while" is a subordinating construction, not a coordinating one, so it doesn't have the same strict parallelism requirements as does "but".
B是while做从属连词，接ing做伴随状语，相当于while接从句省略了逻辑主语并将表主动式的谓语动词变成ing形式。and,but,or这种并列连词连接的是第二个主句，做省略时，要求前面的句子有相同的成分才可以省略。
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