有一天,我考朋友一个脑筋急转弯题。我问: “有一个女孩从海边的沙滩上走过,她的身后为什么没有脚印?”朋友顿了顿问: “当时天黑了吗?”我说:“没有天黑。”朋友回答说: “如果天黑了,连人都看不见,自然看不到沙滩上的脚印。”朋友说得有点道理,但我摇头说不。“那么,是黄昏的时候吧?”朋友接着问。我有点不懂,问: “这有什么关系?”“如果是黄昏,开始涨潮了,潮水就把脚印冲刷掉了。” One day, I tested my friend’s brain teasing question. I asked: “Is there a girl walking on the beach by the sea, why are there no footprints behind her?” The friend paused and asked, “Is it dark at the time?” I said, “It’s not getting dark.” The friend replied: “If it gets dark, even people can’t see it. Naturally, we can’t see the footprints on the beach.” The friend made a point, but I shook my head and said no. “So, is it when evening?” the friend asked. I don’t know a little bit and asked: “What does this have to do with it?” “If it was dusk, it started to rise, and the tide flushed away the footprints.”