杨二叔请教一题比较结构

杨二叔

看完比较结构的总结帖子以后，对此题的比较开始confusing，prep破解版第一题：
To meet the rapidly rising market demand for fish and seafood, suppliers are growing fish twice
as fast as their natural growth rate, cutting their feed allotment by nearly half and raising them
on special diets.

(A) their natural growth rate, cutting their feed allotment
(B) their natural growth rate, their feed allotment cut
(C) growing them naturally, cutting their feed allotment
(D) they grow naturally, cutting their feed allotment
(E) they grow naturally, with their feed allotment cut  

此题中suppliers are growing fish twice as fast as they grow naturally.  句子结构是主系表，按照比较结构总结中的分类，此题应该是宾语比较？？？ 那growing fish 和 they grow naturally怎么对等？
要不然是主语比较？？？ 主系表结构主语比较，后面的谓语动词不是应该省略吗？
难道，难道是句子和句子比较？？？

巨confusing，求解

Luxe

这题 貌似选c吧。。。。。。。。

杨二叔

楼上的童鞋，你选错了，哈哈，正确答案是D