题目选项分析

Industrialization and modern methods of insect control have improved the standard of living around the globe while at the same time introducing some 100,000 dangerous chemical pollutants that have gone virtually unregulated since they were developed more than 50 years ago.

Industrialization and modern methods of insect control have improved the standard of living around the globe but at the same time introducing some 100,000 dangerous chemical pollutants, having gone virtually unregulated since they were developed more than 50 years ago.