题目教室里有7排位子,每排7张,每张位子上坐一个学生,如果一周后,每个学生都必须和他相邻(前、后、左、右)的某一同学交换位子,问这种交换可能成功吗?为什么?这是一道奇偶性问题．如将各个座位依次编号如图1所示,可以看出：奇数的前后左右都是偶数,偶数的前后左右都是奇数．按规定的方法交换位子,必定是 The subject classroom has seven rows of seats, seven in each row, one student sitting in each seat, and after a week each student must exchange seats with a classmate next to him (front, back, left, right) , May this exchange be successful? Why? This is a parity issue. As the number of each seat in turn as shown in Figure 1, we can see that: Odd before and after are even, even before and after are odd. The exchange of seats according to the prescribed method must be