书面表达。
北京正日益成为一个国际化大都市，作为北京市民，请同学们根据以下内容，以“Keep Our City Clean"为题；向包括外国侨民在内的全体北京居民写一份保护环境的倡议书吧。
Things you ever saw: cars producing smog on the street,people throwing things everywhere,leaving water taps on after using them, Things you will do:not to throw rubbish,turn off the water tap after using it,go to school by bike/bus instead of by car,not to use plastic bags,
要求：
1. 语句通顺、语法正确；2. 70词左右。
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