The old woman is _____weak ____look after herself.填too to还是so that ,说明为什么

题目

The old woman is _____weak ____look after herself.填too to还是so that ,说明为什么

答案

The old woman is (too) weak (to) look after herself.
too to 结构构成的是简单句,而so that构成的是从句,如：
The old woman is so weak that she can't look after herself.