21.  In my opinion, the most important reason is the enconomy in the developing countries has grown.

22.  Besides the above the more important reason is science has developed fast, and the level of medicine is more high than before.

23.  Certainly, that more and more people lay great emphasis on their health is the another important reason.

24.  First, the improvement of economics is the most important reason.

25.  One of the most important reason is that the people's living condition is very poor.

26.  I think there are two important reasons.

27.  The important reason was that the food was not enough to so many people in 1960.

28.  And the developed contries took hold of the world econimic , that made the most developing countries's people in deep trouble.Now, the developing countries's people stand up.

29.  As last , the world is relatively peaceful, which also is a important reason of the change.

30.  There was 200 deaths per 1,000 births in 1960.