Why do people plant trees every year?——(keep) our air clean

Why should people plant trees? Why do people plant trees every year?——(keep) our air clean Why should people plant trees?的回答 why do people lie? why do people have pets? why do people need hobbies? Why do people drink 全文 why do people watch boxing why do people go bed? why do people always far why do people need people是什么意思 when do people often plant trees?改为被动语态 Do people usually plant threes in winter?怎么回答 英语作文《why do people trive》急 why do you think people cheat? . Why do people need to play sports Why do some people so hypocritical? Why do more people love basketball?