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.
