It appeared that he had a happy childhood.
It made us very happy that she was saved.
It is +形容词+从句
It is certain that free medical care will be given to most people in our city. 我们城市的多数人将享受免费医疗，这是一定的。
It is obvious that he has been treated.
It is +名词+从句
It is common knowledge that the moon cannot give out light. 月亮不会发光，这是常识。
It is a surprise that you gave such an answer to the question. 你对这个问题作了这样的回答，令人吃惊。
It is said that Jack has been to Europe.
It was reported that a new park will be built.