根据句子意思，用括号中所给词的正确形式填空，每空一词。

1. The young man was too late, but              (luck), he caught the train.

2. I felt bored because of this              (bore) story.

3. If you do more exercise, you will be              (slim).

4. She is one of the best              (run) in our school.

5. The dish             (tasty) very nice.

请简要阐述我国民族区域自治制度的基本内容以及实行民族区域自治制度的必要性。