EXAMPLE 다음 글 바로 앞 문단의 내용으로 가장 자연스러운 것은?

Another factor of population growth is the death rate, which has decreased worldwide. Over the past few hundred years, changes in agriculture have made more and better foods available throughout the world. Improvements in the quality and availability of medical care have wiped out many deadly diseases and contributed to an increase in the life span of the average person. Today physicians can effectively treat diseases that once killed hundreds of thousands of people. Better nutrition and health care have dramatically reduced infant mortality. As a result, the human population has grown so quickly.

 ① 인구증가의 요인        ② 의학 발달의 원인

 ③ 농업 발달의 요인       ④ 사망률 증가의 요인

 ⑤ 공해 증가의 원인