ＴＴＧＷＤ２３一直存在的疑问

ＴＴＧＷＤ２３

Q13:

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

为什么是Ａ，他比较罗嗦不是？？

Ｃ不行么，在ＧＷＤ里也有否定用 as ..as 的

as 。。。as比较对象要对等

前面是花岗岩（it做代词），as。。。as后面是不定式

这里显然式so that更好

A is the best answer among  the five choices

顶！