根据所给中文意思完成句子,每空只填一个词。 1. 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.