阅读下面短文，将短文中划线部分的句子翻译成中文。

It is believed that short-sightedness（近视）is caused by screen use, watching TV or reading in weak light. Researchers have found something different. They advise children to spend two or three hours playing outside each day. It can reduce children's chance of becoming short-sighted.

The research shows that sunlight is good for people's eyes. Playing outside can prevent people from becoming short-sighted. A famous researcher, Ian Morgan 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. "

So be outdoors. It doesn't matter if that time is spent having a picnic or playing sports.