To make our city more beautiful,rubbish mustn't be thrown into the river.为什么用的是mustn't be thrown,而不能用can't throw?

how to make our city more beautiful 4.Let’s try to make our city __________.(save) A policeman helps to make our city a ( )place.(safety) It's our duty to make our city much_____A.dirty B.clean C.dirtier D.cleaner 急,想办法think of a plan to make our city cleaner a急,想办法think of a plan to make our city cleaner and greener. plant more trees to make our city greener为什么后面接to How are we going to make our city cleaner and more beautiful? What can we do to make our city more beauitful and cleaner 要作文! 以Try to make our city more beautiful写一篇短文 We should plant a lot of tree to make our city beautiful.The m______trees,the better. We should plant more trees to make our city more b( ) to make our city cleaner这文章怎么写?至少5句话1.00之前务必回答 it's necessary for us to do someting_______(make)our city cleaner A policeman's job is ________ our city a safe place.(to make making) the police help to make our city a safe place __________do the police ____? 列句：In order to make our city green ,many more trees need planting.为什么? to make our city cleaner这文章怎么写?至少5句话1.00之前务必回答 My father tries to make our city asafe place.(保持原以不变）