请大n们指点一下这道语法题，有点晕。谢了！

The particular design of muscles and bones in the neck and limbs of the turtle allow that it can draw in its exposed parts such that an attacker can find nothing but hard shell to bite.

A.      allow that it can draw in its exposed parts such that

B.      allow it to draw in its exposed parts, and so

C.      allows for it to draw in its exposed parts and that

D.     allows that it can draw in its exposed parts, and so

E.      allows it to draw in its exposed parts, so that

正确答案是D，但我不知道E为什么不对，是不是因为“so that +情态动词”是目的状语从句，而这里只是表示结果，所以用so that不对？请NN指教！！

那D项that引导的从句就使it明确指代turtle了嘛？我不这么认为，那E到底错那了？

我也想知道.NN们请指教.

E选项 it 确实有指代问题,但正确选项it好象也应优先指代主语:the design of muscle.

我认为这题的主要问题应该是E中的结果壮语从句的SO THAT前面不应该有逗号。

在结果壮语从句中，通常只见过WITH THE RESULT THAT 引导的从句前有逗号。