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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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while和 at same time 不是重复的意思吗？还是while在本句中不是同时的意思？
while这里做连词，正常情况while做连词有两种作用：
1，during the time that，当。。。的时候
2，表示对比，轻微的转折。这里应该是第二种意思能够加at the same time .
当然我做题的时候是靠排除DE来消除这个疑惑的，因为but做并列连词只有第二个句子的主谓和前面完全一致才能省略，前面是improved，后面是不能省略主语+are的，所以这时候再来看while表然而加个at the same time 意思挺合理的，然后就是前面说优点后面说缺点，while单纯表示当。。。的时候的话语义表达不够好
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