Make a plan for the day and write an invitation letter to your classmates.

为这一天订个计划并且给你的同学写封邀请信。

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However in some occasions such as inviting somebody else to participate my birthday party, I'll write an invitation letter, since it is more formal way to inform.

然而，在一些非常正式的场合，比如：邀请别人参加我的生日会，我也会写要邀请信。毕竟这是一种更为正式的方式。

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Write a letter to a friend refusing an invitation to a party. Supply a suitable Introduction and Conclusion. Use the following ideas to write your Purpose.

朋友邀请你去参加一个聚会，写封信谢绝这一邀请。写出恰当的引言和结束语，“目的”部分按以下思路写。

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