根据所给汉语提示完成句子。

1. Soon they _____ _____ (飞越) the high mountains and landed safely in Tibet.

2. Don't worry about my parents. They are both in _____ _____ (身体健康).

3. Do you know _____ _____ (发生什么) outside just now?

4. Some of my friends are interested in _____ _____ (集邮).

5. Is it possible for us human being to leave all the animals in the _____ _____ (自然环境)?

更换空滤、机滤、并在燃料箱中加入燃料稳定剂和（）剂。