【正确答案】[范文]
   
   As we all know, friends are a crucial part of our life. Have you even thought of the fact that one can be judged by the friends one makes. As far as I'm concerned, it is meaningful and significant in three respects.
   Firstly, it is common that friends of the same kind often gather together. In other words, if people share the same aim or interest, they will absorb each other. Just as the saying goes, "Birds of a feather flock together." Secondly, if two have different attitudes towards life, their friendship will not last long. Last but not least, we are free to choose friends thus it is not difficult to judge one by the company he keeps.
   The theme of the saying is that we should be extremely careful in choosing friends. For the ones who have many bad habits, vulgar tastes and no ambition, we should keep a distance with them. On the contrary, we should try to make friends with upright and learned people, who will benefit us a lot in our future life.

【答案解析】
   这是一篇分析型的论说文。要求结合“知其人，观其友”这句话，对选择朋友的重要性进行分析。根据题目要求，全文可以安排如下：
   第一段概述现象，引出下文讨论的话题“知其人，观其友”。
   第二段从几个方面分析论证为什么要慎重选择朋友。
   第三段总结全文。