4-4=?

one day, the teacher inquired peter: how much is four minus four? peter was tongue-tied.

the teacher got angry and said: what a fool! you see, if i put four coins in your pocket, but there is a hole in your pocket and all of them leak out, now what is left in your pocket?

the hole, replied peter.

四减四等于几？

一天，都是问彼德：四减四等于几？彼德张口结舌答不上来。

老师生气地说：真笨！你想，如果我放四个硬币在你的口袋里，但你的口袋里有个窟窿，结果四个硬币都漏掉了。那么，你的口袋里还有什么？

窟窿，彼德答道。