1.We'd better not liter in the street.
2.We should not spit in public places.
3.Everyone ought to do his bit to keep the public places clean.
4.We should fill in our kids' mind how important the enviroment is.
5.The concept of enviroment protection should be written in books for children in kindergarden.
6.When you walk your dog,if your dog dropped something in the street,you ought to clean that.
7.Men who smoke had better take along a bag for collecting ash when get out.
8.If you are suffering from a cold ,you should bring along a pack of tissue anytime.
9.We'd better not build so many factories around here,or else the enviroment would be worse.
10.If someone is contaminating the enviroment,you ought to stop him.