根据所给中文意思完成句子，每空只填一个词。
1. 董先生无论什么时候睡觉，总也睡不够。
Mr Dong doesn't get enough sleep _______ he_______ to bed.
2. 查一下你们是否都有飞机票。
_______ _______ you've got the air tickets.
3. 我叔叔以前是个司机，而现在他是工程师。
My uncle _______ _______ be a driver, but now he is an engineer.
4. 轮到你在会上发言了。
It's _______ _______ to speak in the meeting.
5. 假如每个人都为保护环境做出自己的贡献，这个世界将变得更加美丽。
The world will become much more beautiful if everyone ______ a contribution
to _______ the environment.
