It is+adj+to do sth和it+adj+to do sth 的区别：
1、 It is important to drink enough water every day.
it形式主语，没有意思的。to drink enough water every day，真正主语。意思是：每天喝足够的水很重要。,而谓语is important，使用了形式主语，而把真正主语放在后面，所以句型：It is+adj+to do sth的意思是：做某事怎么样。
2、 Doctors think it is important to drink enough water every day.
这时候It is important to drink enough water every day.
是宾语从句,作think的宾语.因为think 可以形成think+ 宾语+宾语补足语,所以此句可改成Doctors think it important to drink enough water every day。也就是少了be动词is，此时，it是形式宾语，important为宾语补足语to drink enough water every day为真正宾语。
拓展资料
It is+adj+doing sth
1、Germany should understand this because that is precisely what it is doing.
德国应理解这点，因为这正是该国正在做的事情。
2、How hard it is doing this.
这些事做起来行难。
3、Fortunately, it is doing so.
幸运的是，西方正在这么做。
4、With three built-in sensors, the iPhone knows more about what it is doing than I do.
使用三个内置感应器，iPhone知道我要干什么。
5、It is doing this with effortlessly simple products that are a pleasure to use.
它这样做的轻松愉快的是使用简单的产品这一点。
it+adj+to do sth
1、How difficult is it to do business with the company?
和那家公司做生意有多难？
2、You still need to test that the generated code actually does what you expect it to do, however.
然而，还需要测试所生成代码真的完成了您所期望的任务。
3、And how do you use it to do better work?
还有，如何利用它来达到更好的工作效果呢？
4、Would you choose this field if you had it to do over again?
如果再来一次，你还会选择这个行业吗？
5、In an OO system, a class shouldn't exist unless there's something for it to do; there must be responsibilities ( operations).
在OO系统中，类如果没有事情可做就不应该存在；必须有职责（操作）。
