Fill in each blank with a proper word chosen from the box. Each word can be used only once. Note that there is one word more than you need.

A． counting B． determined C． distraction D． environmental E． focus    F． modified G． naturally H． performing I． worsening J． comprehensively   K． significant

Myopia， or short﹣sightedness， is a condition in which distant objects appear blurred （模糊的）， but closer objects can usually be seen in sharp focus． Its biological basis is an eye that， during childhood， has grown too long for its optical power． The focal plane for images of distant objects ends up in front of the retina， causing out﹣of （1） 　 　perception．

   Myopia was once regarded as almost totally genetically （2） 　 　． But its prevalence （流行） has increased spectacularly in urban mainland China， Hong Kong， Taiwan， Singapore， Japan and South Korea， where 80﹣90% of those completing high school are now short﹣sighted． This is up from 20﹣30% only two generations ago． Since gene pools do not change that fast， these massive changes must be due to（3） 　 　change． In 2005， we （4） 　 　reviewed the research on myopia and found a correlation with education． （This was not a particularly novel insight： such a link was supposed as far back as Kepler in 1604．） We found locations with a high prevalence of myopia were all top performers in surveys of international educational outcomes．

   Fortunately， not all high （5） 　 　locations， Australia among them， showed a high prevalence of myopia． This shows that high educational outcomes do not necessarily lead to myopia． We also hypothesized that all human population groups had a tendency to develop myopia under particular environmental conditions． Indeed． North America and Europe have seen growing rates of myopia， although they are still nowhere near as high as in East and Southeast Asia．

   A common cutoff for high myopia is 5 diopters （屈光度）． This means vision is blurred beyond 20cm from the eyes． Such severe or high myopia increases with age and can lead to visual impairment that can't be corrected． The prevalence of high myopia has now reached 20% in young adults in East and Southeast Asia， which foreshadows major increases in visual （6） 　 　and blindness as these young adults age． So prevention of myopia has become crucial， particularly for East and Southeast Asia．

Australia has （7） 　 　low levels of myopia with a lifestyle that emphasizes outdoors activities． Young children report spending two to three hours a day outside， not （8） 　 　time outdoors at school． However， there are formidable barriers to achieving this benchmark in locations where spending time outdoors is seen as a（n）（9） 　 　from study． Policy responses must therefore also aim to slow the progression of myopia， the phenomenon in which mild to （10） 　 　myopia becomes more severe during childhood． There is currently controversy over whether time outdoors slows progression， but strong seasonal effects on progression suggest that it may．