请教一道prep SC 没给答案的~prep 04

4. Although the turtle has been toothless for more than 150 million years, in some contemporary turtle species the moderately sharp and jagged edges of their horny jaws function for teeth.

A. their horny jaws function for teeth

B. its horny jaws function for teeth

C. its horny jaws function as do teeth

D the horny jaws function as teeth do

E the horny jaws function as teeth

我选D得~~

大家选什么呢？？

现在觉得选E了

as teeth do中的do和前面没有动词对应的~~