1. 以下图为依据描述发展中国家的期望寿命(life expectancy)和婴儿死亡率(infant mortality)的变化情况。
2. 说明引起变化的各种原因。
Health Gains in Developing Countries
范文：
In the developing countries GREat changes took place in life expectancy and infant mortality in the period from 1960 to 1990. In 1960 life expectancy was very low, while infant mortality ws very high. However, in 1990 life expectancy increased, whereas infant mortality 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 developing countries suffered hunger and were exposed to the elements. Nowadays they are well fed and housed. Naturally they live longer than before. Besides, the medical condition was also improved and so the adequate medical treatment ensures the adults' health and reduces infant 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, the national independence and social stability are responsible for these changes.
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