The link between health and income seems pretty uncontroversial.【C1】______all, healthy people can work longer and harder than sick people. Healthier children are【C2】______to stay in school longer and learn more,【C3】______more when they enter the workforce. Even across countries the【C4】______seems clear: those with better health are【C5】______richer. The researchers of the Massachusetts Institute of Technology are skeptical about the notion【C6】______healthier countries are richer, because countries with【C7】______incomes may simply spend more on health. To investigate, they needed to study health improvements that were not【C8】______by economic growth in the countries concerned. Beginning in the 1940s, several medical【C9】______involving penicillin (青霉素) and DDT (滴滴涕) made it easier to【C10】______diseases—such as tuberculosis (结核病), malaria (疟疾) and yellow fever—that【C11】______people in developing countries. Because these ideas【C12】______in the rich world and were spread by【C13】______such as the WHO, any improvement in【C14】______they led to would have been unconnected with prior improvements in the economic【C15】______of poor countries. This international revolution in public health【C16】______lead to substantial increases in life 【C17】______in poor countries by the 1950s. However, the researchers found that income per head actually【C18】______when life expectancy went up. The reason was that increased life expectancy led to a larger population using a【C19】______stock of things like land and capital,【C20】______depressing income per person.