Dear schoolmate,
亲爱的同学：
I don't know who you are, but I am really grateful to you. Yesterday, I lost my library card in the playground. I didn't realize it until I got home after class. I was so upset, because it's too bothersome to register another one. But today, when I got to school, the guard told me that someone picked my library card and gave it to him. I was so exciting to hear the news. You did not leave your name and I don't know who you are. I am really appreciated for what you did.
我不知道你是谁，但我真的很感激你。昨天，我在操场上弄丢了我的图书证。直到我下课后回到家我才意识到这件事。我很难过，因为注册另一个证太麻烦了。但是今天，当我到达学校，门卫告诉我有人捡到了我的图书卡并交给了门卫。我很高兴听到这个消息。你没有留下你的名字，我不知道你是谁。我很感激你所做的。