四级作文题目： Health Gains in Developing Countries
　　It can be seen from the charts that there have been dramatic changes in life expectancy and infant mortality in developing countries in the past decades. As the chart shows, people's life expectancy soared from 40 years old to 60 years old from 1960 to 1990. Meanwhile, infant mortality declined from 200 to 150 deaths per thousand births.
　　The changes in the charts may be attributed to a number of factors, but the following are the most critical ones. First, developing countries' economy has been developing at a considerably high speed in the past decades. Therefore, people have more extra money to improve their health. Secondly, the advances in medical sciences and boom of medical industry provide citizens with more opportunities to cure their diseases. Last but not least, people have attached greater importance to their quality of life, thus they have spent more money and time to build up their bodies.
　　In a word, these charts are perfect indexes of developing nations' fast expanding economy and people's rising standard of life. Although a series of problems have arisen in the process, it is reasonable for us to believe that they can be solved in the near future with effective measures taken by both the government and the public.
　　(或If this trend continues, developing countries will soon approach the developed countries in terms of health care. People will live longer and healthier lives. The result of this will be happier and more productive populations.)