this graph tells us the changes in the life expectancy and infant mortality in developing countries between 1960 and 1990. we can see that the life expectancy in 1960 was about 40 years whereas in 1990, it increased to about 60 years. in the meantime, the infant mortality rate dropped from 20off00 to 10off00.

　　there are many reasons for these changes. first, thanks to the advances in science and medicine, people are receiving better health care services than they used to. secondly, with the development of economy, people are better off today.

　　so they can attach much importance to their diet. thirdly, owing to the increasing awareness of environment protection, measures are taken to solve the problem of pollution. all these are beneficial to people's health which certainly prolonged their life expectancy.