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一天,老师告诉他的小学生只有两样东西相同才能相减,“比如我们不可能从6个香蕉里取出5个苹果来,是一个道理的。”
One day, the teacher told his pupils that only two things can be subtracted from each other. “For example, it is impossible for us to take five apples from six bananas.”