SC 比较一道题

小小白一只

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

这道题目为什么是D啊， suppliers are growing fish 与 fish grow naturally 感觉没有可比性啊，虽然语义上D是对的。。

kluivert

小白觉得是动词与动词比较
Are growing 和 grow
我读完题就直接在找有完整谓语动词的比较
后面的,Ving 是对preceding clause 的解释，如何做到are growing twice as fast as ...