单选题 If x and y are different prime numbers, each greater than 2, which of the following must be true?Ⅰ. x+y ≠91Ⅱ. x-y is an even integer.Ⅲ. x/y is not an integer.
【正确答案】 E
【答案解析】x，y都是大于2的质数，那么x，y必然都是奇数，所以两者之和必然为偶数，那么Ⅰ正确，两者之差也是偶数，Ⅱ正确，而由于x，y互质，x/y必然不是整数。因此E为正确答案。