中小学生的近视问题比较严重，请你用英语简单讲述这一现象的原因，并对同学们该怎样保护视力提出二、三条建议。

不唯一

Last weekend, I had an interview with Professor Wang, an eye-doctor, concerning about short-sightedness of school children in China. according to Professor Wang,slightly more than half of the school children in our country are short-sighted, rankingthe first in the world. He also pointed out that the causes for short-sightedness are so complicated that no medicine can cure short-sightedness. He suggested that schoolchildren avoid overuse of their eyes and do more out door activities or do eye exercises. He particularly reminded us that how to hold a pen is also related to short-sightednes.