Dear Bob

Dear Bob,
       I am sorry to say that I cannot go to the bookstore with you on Friday afternoon.I have just found that I have   to attend an important class meeting on Friday afternoon.I hope the change will not cause you too much trouble.
       Shall we go on Saturday afternoon?We can set out early so that we will have more time to read and selections.If it is you convenient,if not,let me know what time suits you best.I should be avaiable any time after school next week.
       I looking forward to your reply.I wish you and your family good health and happiness.

### 第三档 13-18分

#### 评分：
这篇作文基本完成了试题规定的任务，并提及了关键的内容要点。语法结构和词汇满足了最低要求，但存在一些语言错误，影响理解的程度有限。

#### 不足之处和建议：

1. **第一段：**
   - “I am sorry to say that I cannot go to the bookstore with you on Friday afternoon.” 句子结构正确。
   - “I have just found that I have to attend an important class meeting on Friday afternoon.” 改为 “I just found out that I have to attend...” 更为自然。

2. **第二段：**
   - “Shall we go on Saturday afternoon?” 使用了适当的询问方式。
   - “We can set out early so that we will have more time to read and selections.”
     - “selections” 可能是笔误，建议改为“choose books”或“browse selections”。
   - “If it is you convenient, if not, let me know what time suits you best.” 改为 “If it is convenient for you, let me know if another time suits you better.”

3. **第三段：**
   - “I looking forward to your reply.” 应为 “I am looking forward to your reply.”
   - “I wish you and your family good health and happiness.” 结尾恰当。

#### 总结：
整篇文章的结构合理，基本传达了信息，但在表达上有一些小错误。建议多加注意时态和拼写错误。