could not but后面是do还是to do来着

could not do but do
could not ..(除do外其他动词)but to do

不得不：can't but do    can't的过去式couldn't

不得不有三种：can't but do, can't help but do, can't choose but do

这是从我书上拍的。外研版必修三108页：

do

do
I could not but feel disappointed at hearing the news.

to do