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. A. while at the same time they have introduced some 100,000 dangerous chemical pollutants, having B. while at the same time introducing some 100,000 dangerous chemical pollutants that have C. while they have introduced some 100,000 dangerous chemical pollutants at the same time, which have D. but introducing some 100,000 dangerous chemical pollutants at the same time that have E. but at the same time introducing some 100,000 dangerous chemical pollutant, having 这道题答案是B,但是A哪里错呢???很困惑地说。。。