英语翻译这本字典对那些学英语的人来说很有用 be of 要我们告诉你什么时候出发什么时候到达是很困难的 it主语 发生在

1.This dictionary is of great use to those who are learning English.
2.It is difficult for us to tell you the departure and arriving time.
3.What happened to him has proved to be a huge success.
4.We would put off the meeting till next Friday.