旁证每个学期开始的时候,布告板上总贴有出售旧教科书的告白。其中一张写着: “《心理学入门》。五十元。从未用过。”署名旁又写着:“必须卖出。”第二天,那张告白上加了一张条子: “价钱公道。可是你真的从来没有用过?”签名是:“可能的买主。” At the beginning of each semester at the beginning of the semester, there was a confession of selling old textbooks on the board. One of them read: “An Introduction to Psychology. Fifty yuan. Never used.” Next to the signature, it read: “You must sell.” The following day, a note was added to the confession: “ The price is fair, but you really never used it?” The signature is: “Possible buyer.”