2. 外语
  3. If p is a prime number greater than 11, and p is the sum of the two prime numbers x and y, then x could be which of the followin

If p is a prime number greater than 11, and p is the sum of the two prime numbers x and y, then x could be which of the followin

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问题 If p is a prime number greater than 11, and p is the sum of the two prime numbers x and y, then x could be which of the following?
选项 A、2
B、5
C、7
D、9
E、13
答案A
解析 若p是比11大的质数(prime number)，且p等于两个质数x，y的和，则x可能是下面的哪一个?
解：本题的正确答案为(A)。考生在解答此题时，应比较熟悉质数、奇数与偶数之间的相互关系。p是比11大的质数，所以p必是奇数。而p同时又是两质数的和，由于一个奇数只可能是一个奇数与一个偶数之和，故x、y中必有一个是2(因为除2以外，其他质数均为奇数)。若y取2时，则x无论取五个选项中的哪一个都不能满足题意，所以必有x=2。
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