One possible version :

Dear Sam ,

Thank you for your concern. I am glad to tell you something about what you asked about our college entrance examination .

The college entrance examination falls on June 7and June 8 every year ,and the subjects that we should prepare for are different depending on each province .Generally speaking , we are busy reviewing and preparing for it the moment we enter senior three ,which is considered a vital period .With the exam approaching , most students will feel nervous and upset .But by now when I am sitting the exam , I feel calm ,because I think the exam is neither too easy nor too difficult . I am sure I will get a good result .But whatever the result is, I will face it calmly. After all , I have made every effort ,and I won’t regret .

Best wishes !                                 

Yours ,

Li Xia

题目分析：本篇书面表达要求写一封书信，告诉朋友关于高考的一些情况，属于应用文范畴。书信是同学们非常熟悉的一种写作体裁，而且内容也是同学们正在体验着的高考，并且开头和结尾又已经给出，所以同学们写起来应该是游刃有余。在写作时应注意的问题有以下几个方面：首先，因为内容是同学们正在经历着的关于高考的事情，所以要使用一般现在时或者现在进行时。其次，要尽量使用高级词汇和句型来提高作文档次。此外，写作时也要使用恰当的连接词以使行文连贯，层次清晰。

【亮点说明】本篇书面表达要点全面，语言流畅，时态、人称和标点符号的使用正确，很好的完成了写作任务。在作文中作者开门见山提出自己写信的目的，即告诉Sam有关高考的事情，这种结构安排符合书信类文体的结构安排。在句式方面作者使用了定语从句which is considered a vital period，状语从句whatever the result is, 宾语从句what you asked about our college entrance examination等，而且还用到了Generally speaking , With the exam approaching , After all ,等短语，这些短语和句式的使用有效地增加了文章的亮点，提高了作文档次。