钙基润滑脂主要用于汽车、拖拉机等机械设备上，使用温度范围为（）。

A.－10～60℃

B.－10～100℃

C.－10～140℃

D.－10～160℃

Directions:

The following chart shows the percentage of near-sighted students in Chinese schools. Write an essay of 160～200 words based on the chart. In the composition you should:

1) describe the situation

2) analyze the causes, and

3) give your comments.