We should plant/ cut down trees.
plant
You should throw/ pick up your rubbish into recycling bins.
throw
You should plug/ unplug the TV when you don't watch it.
unplug
We should protect/ harm animals.
protect
We shouldn't waste/ save water.
waste
We should pick up/ throw the rubbish on the ground.
pick up
You should use/ not use public transportation.
use
You don't have to/ mustn't go to school on weekends.
don't have to
You must/ mustn't study if you want to get higher marks.
must
You should/ shouldn't wear a coat, it's cold outside.
should
You have to/ don't have to go to school on time.
have to
You mustn't/ don't have to eat it if you don't like it.
don't have to
She doesn't have to/ should get a car if she doesn't like to go to school by bus.
should
We must/ mustn't connect to the internet to send an e-mail.
must
You shouldn't/ mustn't feed the animals in the zoo. It's forbidden!
mustn't
You have to/ mustn't listen to loud music. It's not good for your ears.
mustn't
