1）can't but do sth 不能（做其他的）只能做这个, 有点have to的意思. 简单来说：不得不做某事，只能做某事. I cannot but study for this exam—it counts for half of our grade! 我不得不为这次考试学习——它占我们成绩的一半! We can't but intervene here, before you throw your life away ...
You use cannot but, could not but, and cannot help but when you want to emphasize that you believe something must be true and that …
Meaning of. cannot but. in English. If we persevere, we cannot but succeed. If we remain true to ourselves, we cannot but …
更多内容请点击：语法-36-5｜can't but do sth - 知乎专栏