在国外论坛上看到的一篇回复,觉得这个解释很有用,这里引用一下 Generally speaking, when you have a "with" modifier set off with a comma, the modifier is usually functioning as an adverbial modifier, which means it modifies the entire clause it is touching, and it usually provides some additional commentary about that clause.
So, in the first case, while the lions are growling, their fur is also standing on end - the "with" modifier about the fur is giving us extra info about when the lions are growling.
That's not quite what's going on in the second sentence. The meaning is more like "though the seniors compose only 25% of the student body, they get 50% of the resources." The first part is not additional information about or an example related to the main clause. Instead, it is part of a contrast being made between the two parts of the sentence.
The other problem with the "wrong" sentence is that it is ambiguous. What does "with only 25% of the student body" mean? The seniors are using 25% of the student body - maybe the freshmen? - to get 50% of the resources? Or the seniors are, themselves, 25% of the student body? 那么这句话应该有两个问题,一个是逻辑意思上不对,with表现得是一种联系,而这个句子本身要表现的是一种对立,另一个问题是会产生歧义,with only 25% of the student body是指的seniors中的25%,还是seniors占学生总数25%