向各位大神请教一道sc题目

wujiaqi3347

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, havinggone 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

这道题正确答案是B，但鄙人不明白B选项的introducing与前面have improved 之间的关系。我觉得应该是这些methods 引起了两个结果，一个是提高生活水平，一个是引起化学污染物，所以C更好些~希望明白这道题的大神帮我讲讲~~~在此谢过啦~

maoshi888

while在这儿表对比，就像你说的一方面improve了standard，另一方面引起污染，while做连词的时候如果主语一致且第二部分的谓语是be的话就可以省略，用while doing，C明显不简练，而且which的修饰有歧义

wujiaqi3347

maoshi888 发表于 2013-8-24 18:03
while在这儿表对比，就像你说的一方面improve了standard，另一方面引起污染，while做连词的时候如果主语一 ...

奥奥，明白了，谢啦