21.  Firstly, we can learn it through all kinds of mess media, such as radio, TV, newspaper, etc.

22.  Everyday news is the most important things about the society that we should know.

23.  It is a very important thing the college students get to know the world outside the campus.

24.  What important thing is that we could serve the society .

25.  We ought to save water, deal with polution , these is the most important thing that we should do .

26.  The most important thing we should do is to let everyone realize the problem and do his own best.

27.  But the most important thing to do is not to waste any of the fresh water from now.

28.  The most important thing is we shall save fresh water and use it efficiently.

29.  The most important thing is creaseing the polution .

30.  Most important thing of all is not to pollute it.