It's very difficult to do sth.做某事很困难 其中It是形式主语,to do sth是真正的主语.如‘
It's very difficult to learn a foreign language.学习一门外语很难.那这个句型是it is to do sth 吗？？？谢谢~~~我英语不太好。。应是：It is +形容词+to do sth.