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 pollutants, having 这里面having可能修饰pollutants，也可能修饰they have introduced some 100,000 dangerous chemical pollutants整个分句，所以having产生了修饰歧义 这大家都知道的prep的一道题目，having修饰歧义是问题之一。
但有道题目： Although ice particles in the upper atmosphere benefit Earth in that they reflect and absorb solar radiation, acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate the destruction of the ozone layer by reacting with chlorofluorocarbons (CFC's). A. acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate B. acting as a global thermostat and thus keeping Earth either from burning up or freezing over, while also accelerating C. act as a global thermostat and thus keep Earth from either burning up or freezing over, while also accelerating D. they act as a global thermostat that thus keeps Earth either from burning up or freezing over, even though it also accelerates E. they act as a global thermostat to thus keep Earth from either burning up or freezing over, but they also accelerate 我在论坛上看到别人的解释是acting一定是修饰主语的，而不是radiation，还给出了解释。（这点我也是这么认为的） If a participial phrase comes at the end of a sentence, a comma usually precedes the phrase if it modifies an earlier word in the sentence but not if the phrase directly follows the word it modifies. The local residents often saw Ken wandering through the streets. (The phrase modifies Ken, not residents.) Tom nervously watched the woman, alarmed by her silence. (The phrase modifies Tom, not woman.) 前人不少帖子也总结过分词的用法，说现在分词放在句尾即修饰的是整个句子或者主句（像OG12TH 第一题） 但是第一道题目为什么存在分词就近修饰的问题呢？不理解是怎么回事，请大家点拨点拨我。作者: elsachialee 时间: 2011-5-23 13:12
我在一个论坛上看到一个老外有这样子一句话，希望对你有帮助。 if there are more than one logical referents, then ing.. form after the clause is incorrect.作者: chasekai 时间: 2011-5-23 13:29
我在一个论坛上看到一个老外有这样子一句话，希望对你有帮助。 if there are more than one logical referents, then ing.. form after the clause is incorrect.
