GWD31-23-13 so as to & so that

Researchers hypothesize that granitic soil is the ideal construction material for the desert tortoise because it is not so hard that it makes burrowing difficult or so soft that it could cause tunnels to collapse.

1. so hard that it makes burrowing difficult or so soft that it could cause

2. hard enough to make burrowing difficult or soft enough as to cause

3. so hard as to make burrowing difficult or soft enough so it causes

4. as hard as to make burrowing difficult or as soft as to cause

5. too hard, making burrowing difficult, nor too soft, so as to cause

答案是A,C哪里错了阿。

自顶一下，等待回答。

这个问题我也好感兴趣啊，请问哪位NN可以回答一下吗，谢谢拉。

先说说我的感觉，C里面有一个错误的用法，enough，记得石林说过enough to这个结构太口语话，在GMAT里面一定是错的。

但是这里关于A我有一个疑惑，既然是or的并列结构，为什么A选项里面的两个parts不平行呢？一个是makes一个是it could cause？