什么情况下用独立主格？以PREP一题为例

Shrinking faster than any other nation's,the projected decline of Japan's population is 17 precent during the next  half century. 

ABD错的明显

C the population of japan is shrinking faster than that of any other nation and is projected to decline by

e  Japan's population is shrinking faster than that of any other nation,with a projected decline at

正确答案是C 语法笔记认为动词decline by比名词 decline at要好，我当时选的是E，我认为E是独立结构，按语法笔记总结的GMAT常考独立结构。请教一下各位E是独立结构吗？如果是的话为什么不优先选择呢？

Shrinking faster than any other nation's,the projected decline of Japan's population is 17 precent during the next  half century. 

ABD错的明显

C the population of japan is shrinking faster than that of any other nation and is projected to decline by（比较结构很工整。我自己总结觉得比较结构越工整越好。gmat比较讲究这个的。还有平行结构也是。）

e  Japan's population is shrinking faster than that of any other nation,with a projected decline at独立主格表伴随原因、状态、条件等。at“以....”by“到....”

似乎独立主格的用法没错吧

the population of japan >Japan's population。