不定式前有
助动词do,to 后面的do需要省略。 连词连接两不定式前面的有do后面的to do的to省略,如: I have nothing to do but watch TV all day long. Tom have no choice but to give it up. 2.用is连接,不定式作
表语时前面主语有do时后面表语to do的to省略,如: What I want to do is stay at home. What I want is to stay with you. 3.注意这里说的前有do后无to的前面的do要是实意动词do,不能是助动词do 规律: 1.but/except前有
实义动词(有些老师也叫行为动词)do的各种形式,but/except后面要用“不带to的不定式(即动词原形),反之需要加to" 2.但是最关键的是在
美国英语中有3个短语can't but do: can't help but do: can't choose but do已经是惯用法了,不能按第一条规律遵守。