You should not laugh at others when they are in trouble改祈使句

You should not laugh at others when they are in trouble改祈使句
___ ____ ____ ___ when they are in trouble.
To plant more tress is important for us改同义句
___ __ for us ___ ___ ___ ___.
I don't know what yo say改祈使句
I don't know ___ ___ ___ say