假定你是李华，David是你的美国笔友。他对中国鼓励使用环保购物袋很感兴趣，来信向你询问此事。请你给他写封回信。主要内容如下：

Yours,

Li Hua

6月5日是世界环境保护日， 请你写一篇以“Lower carbon（低碳）, happier life”为主题的英语短文。

短文要点如下：

Lower carbon, happier life

It’s our duty to save the environment. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Write at least 60 words about“________ is /are important”.(请以“________ is /are important”为题)，写一篇不少于60字的文章。