问大家一个语法题

The particular design of muscles in the neck of the turtle_______________   an attacker can find nothing but hard shell to bite.

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

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

B.
习惯表达 allow sth. to do sth..
A :so本身就可以是连词,为什么还要and呢?

allow that....不对, allow  that只用在表“承认”时， allow that formal to admit that something is true: I allow that there may have been a mistake”。

请指正.

我也觉得是b 对，可答案怎么是第一个呢？想不明白

and so好像有一个idiom,是因此的意思

谢谢charlesbibi提醒了我一个语言点 and so.

不过我还是觉得A不对. allow to好于allow that..

请NN帮忙.