When countries develop economically,people live longer lives.Development experts have long Delieved this is because having more money expands lifespan,but a massive new study suggests that education may play a bigger role.The finding has huge implications for public health spending.Back in 1975,economists plotted rising life expectancies against countries'wealth,and concluded that wealth itself increases longevity.It seemed self-evident:everything people need to be health from food to medical care--costs money But soon it emerged that the data didn't always fit that theory.Economic upturns didn’t always mean longer lives.In addition,for reasons that weren't clear,a given gain in gross domestic product（GDP）caused increasingly higher gains in life expectancy over time,as though it was becoming cheaper to add years of life.Me moreover,in the 1980s researchers found ga ins in literacy were associated with greater increases in life expectancy than gains in wealth were Finally,the more educated people in any country tend to live longer than their less educated compatriots.But such people also tend to be wealthier,so it has been difficult to untangle which factor is increasing lifespan Permanent change Wolfgang Lutz of the International Institute for Applied Systems Analysis in Vienna and colleagues have now done that by compiling average data on GDP per person,lifespans,and years of education from 174 countries,dating from 1970 to 2010 They found that,Just as in 1975,wealth correlated with longevity.But the correlation between longevity and years of schooling was closer,with a direct relationship that did not change over time way wealth does When the team put both these factors into the same mathematical model,they found that differences in education closely predicted differences in life expectancy,while changes in wealth barely mattered Lutz argues that because schooling happens many years before a person has attained their life expectancy,this correlation reflects cause:better education drives longer life.It also tends to lead to more wealh,which is why wealth and longevity are also correlated.But what is important,says Lutz,is that wealth does not seem to be driving longevity,as experts thought-in fact,education is driving both of them Lifestyle choices Some medical professionals may not like these findings,"says Lutz,as they suggest schools may be a better health investment than high-tech hospitals.But RudigerKrech at the World Health Organization welcomes the study."It confirms education as a major social determinant of health,"he says-aconcept WHO actively promotes.But if medical health experts welcome the findings,economists are less comfortable Sangheon Lee,at the UN International Labour Organisation in Geneva,Switzerland agrees education affects lifespan but doubts that simple models like Lutz's can fully resolve cause and effect."It's a very difficult econometric problem,"he says,with health,wealth and education all affecting each other But Lutz says that extreme examples are telling.Cuba is dead poor but has a higher life expectancy than the US because it is well educated.Meanwhile in oil-rich but poorly-educated Equatorial Guinea,people rarely reach 60
What does the word"plot"（Line 1,Para.2）mean?

A To make a secret plan to harm somebody

B To make a diagram that shows how things develop

C To suggest something as a plan or course of action

D To mark the path of an aircraft or ship on a map