industrialization and modern methods对于while用法的疑惑

viewlam

Industrialization and modtern 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 100,000 dangerous chemical pollutants at the same time, and have
d. but introducing some 100,000 dangerous chemical pollutants at the same time that have
e. but at the same time introduce some 100,000 dangerous chemical pollutants, having


对于这题的while我有两个疑惑：
1.while不是代表着“当...的时候”吗，也具有同时的意思，这不就和at the same time句意重复了吗？
2.while不是也有表示转折的意思吗，我看到rule out D的理由都是说因为原意没有转折的含义


恳请NN们赐教～～谢谢！

whyade

谢谢楼上分享。
我看到Ron提到，subordinators有些是可以使用状语从句省略形式（引导词 + 分词 / 形容词），有些必须用完整的状语从句。前者比如although，后者比如even though。

我的问题是：还有哪些subordinators是必须用完整的状语从句，不能只加分词/形容词的？
望NN回答。

emmahiggins09

曼哈顿RON大神的帖子，楼主请自便

https://www.manhattanprep.com/gmat/forums/industrialization-and-modtern-methods-of-insect-control-have-t460.html