据下列句子及所给汉语注释，写出空缺处各单词的正确形式。（每空只写一词）

1. I wonder why Jack hasn't w______ to us recently. We should have heard from him by now.

2. There was no lift and we had to climb six f______(一段楼梯) of stairs.

3. People should wash ______(定期) to ensure personal health.

4. I think you o_______ us an apology for not informing us of the important news in time.

5. He told us that the _______(北部) part of his country had many mountains.

6. We reached our destination, tired and ______(饥饿).

7. Exercise firms the body, strengthens the muscles, and prevents you from gaining w______.

8. The whole day we unpacked the boxes, filled the cupboards and tidied, until we were ______ (极其) tired.

9. The house is h______ by trees, so it is hard for us to find it.

10. He left his village school and ______ (教) himself while working in a factory.