这句英语句子里为什么加to?是不定式还是介词？

Question

1.It is good to study hard every day.
2.It is bad to drink beer every day
这里的to有什么作用？

Answer 1

这两个句子中都是动词不定式。

to 后面是动词的话，就是动词不定式。

to后面是名词，代词等，就是介词。

这两句话的动词不定式是真正的主语，it 是形式主语。

可以改写为:

To sdudy hard every day is good .

To drink beer every day is bad .

Answer 2

这两个句子都是不定式，动词不定式作主语。而不是介词。

It is good to study hard every day.真正的主语是：to study hard every day.

2.It is bad to drink beer every day。真正的主语是：to drink beer every day。

Answer 3

固定搭配，be good to do sth是做某事有好处或有益