too……to和so……that的语法结构

题目

too……to和so……that的语法结构
例如He's too young to join the army.这句中to join the army在这句中作什么了?
还有She is so young that she can't look after herself.这句中that后面算式引导从句吗?如果是那是什么从句?

答案

to join the army.和that she can't look after herself 都是做状语.这二个句型可以互换:He's too young to join the army=He's so young that he can't join the army