根据句意及首字母提示在横线处填上恰当的单词，使句子意思完整，语法正确。

1. No one is allowed to break the rules.n our school.  We can only o_______them.

2. Five days has passed, he hasn't r_______to my letter.

3. Work hard, or you can't a________your dream.

4. Mr Zhang has t________English in our school for 20 years. His students are all over the world.

5. What's the main p________of the passage?

6. All the students have their own hobbies,  but some of  them can g_______in the way of their 

schoolwork.