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　　Spending two or three hours playing outdoors each day can reduce a child's chance of becoming short-sighted, a research shows．It challenges (挑战) the belief that short-sightedness is caused by computer use, watching TV or reading in weak light．

　　The Australian government researchers believe that sunlight is good for people's eyes．They compared the vision(视力) and habits of 100 seven-year-old children in Singapore and Australia．In all,30％of the Singaporean children were short-sighted－this rate(比率) was ten times higher than Australian children．

　　Both groups spent a similar amount of time reading, watching television and playing computer games．However, the Australian children spent an average(平均) of two hours a day outdoors－90 minutes more than the Singaporean children．

　　Professor(教授) Ian Morgan, from the Australian Research Council's Vision Centre, said, “Humans are naturally long-sighted, but when people begin to go to school and spend little or no time outdoors, the number of short-sighted people gets larger．We're also seeing more and more short-sighted children in cities all around the world－and the main reason may be that city children spend less time outdoors．”

　　Daylight can be hundreds of times brighter than indoor light．But why does playing outside prevent us from becoming short-sighted? Scientists believe that natural light has a special chemical(化学物质) which stops the eyeball from growing out of shape and prevents people becoming short-sighted．So be outdoors．It doesn't matter if that time is spent having a picnic or playing sports．

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