It was early May. As soon as Sophie got home from school. She ____ (打开) the mailbox at the gate. There was only one ____ (信) in it and it was for Sophie. It looked really ____ (奇怪的), because the envelope(信封) didn't say who it was from. There was no stamp on it, either.

    Sophie took out the paper. It read, "Who are you?" Nothing else, only the three words, written by hand and followed by a large question mark. "Who wrote this?" Sophie said to ____ (她自己). "Maybe a naughty(淘气的) child in the neighborhood, I ____ (猜测)."But she couldn't stop thinking about the question. After half an hour, she said, "Why am I ____ (浪费) my time on it? I'll not think about it ____ (再也)." However, the next day Sophie ____ (注意到) another letter in the mailbox. In it there was only one sentence, "Where does the world come from?"

    Why did someone write to Sophie? What did the questions ____ (意思是)? Could Sophie find out the ____ (事实)? I think maybe you should find out the answers in the famous book, Sophie's World, by yourself.