题目内容：

假如你是中学生李华，你的美国朋友Jack在上次给你的电子邮件中抱怨自己最近眼睛近视了。请你给他用英语回一封电子邮件，内容如下：

1．介绍一下你们班同学的情况；  2．分析一下造成你们班这种情况的原因；

3．帮Jack出点儿保持眼睛健康的主意。

注：1．字数120-150；邮件的开头和结尾已为你写好。

2．近视：shortsighted  adj.  shortsightedness n.

Dear Jack，

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

                                                                                   

Yours sincerely         

Li Hua