One possible version：

Dear Editor，

I'm writing to tell you about a heated discussion among us students in our school about whether students of Senior 3 should take physical exercise.

55% of the students think that we should take physical exercise every day, such as doing morning exercise, playing table tennis or basketball, etc. It can build our body, keep us healthy and reduce illnesses. Meanwhile, it can make us completely relaxed for a better learning effect.

However, 45% of the students are against that. They complain that taking physical exercise is a waste of time. It can make us tired or feel too excited for further learning. More over, we may get hurt during the play. I personally think that proper physical exercise is necessary but never too hard.

Yours sincerely，

Li Hua

题目分析：此篇书面表达要求写一封信来介绍班级讨论情况。对于书信的格式同学们都非常熟悉，写作时只需将要点表达清楚。但是在介绍要点时，一定要注意语言的流畅，而且要恰当使用连接词以使语言连贯，上下文衔接自然。在时态方面，因为是介绍人们的观点，所以可以使用一般现在时。此外，在结构安排上可以使用三个段落来分别介绍赞成观点、反对观点和自己的观点，这样使文章结构清晰。

【亮点说明】本篇范文采用三段式结构，开篇提出写信的目的，然后两段分别介绍对体育锻炼的两种不同观点，这种安排使得文章结构分明，层次清晰。文章在句式方面，既有简练的短句，又有涵盖内容丰富的长句，这种长短句的结合也显示了作者对于语言的把控力。此外文中however、moreover和meanwhile等副词也有效地起到连接上下文的作用，使文章内容连贯，衔接自然。