题目内容：

假定你是李华。下周一至周三因故不能上外教Mr. Smith的英语课，需要向他请假，请你用英文给他写一封电子邮件，内容包括:

1. 解释原因；

2. 请求同意；

3. 弥补措施。

注意:

1. 词数80左右；

2. 可适当增加细节，以使行文连贯。

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