【正确答案】[参考范文]
Health Gains in Developing Countries
In the developing countries great changes took place in life expectancy and infant mor tality in the period from 1960 to 1990．In 1960 life expectancy was very low，while infant mortality was very high．However，in 1990 life expectancy increased，whereas infant mor tality declined．
There are many reasons for the changes，but in general，they come down to three major ones．First，their living conditions were improved．In the old days people in the de veloping countries suffered hunger and were exposed to the elements．Now they are well fed and housed．Naturally they live longer than before．Second，the medical condition was also improved and SO the adequate medical care ensures the adults'health and reduces in- rant mortality．Most important of all，in the early 60s there were constant wars in some developing countries because of the colonial rule and so a lot of people were killed in wars．Nowadays most developing countries have become independent countries and their people live a peaceful life．
In conclusion，better medical care，national independence and social stability are re sponsi ble for these changes．