单选题 If the sum of a set of ten different positive prime numbers is an even number, which of the following prime numbers CANNOT be in the set?
(A) 2
(B) 3
(C) 5
(D) 7
(E) 11

【正确答案】 A

【答案解析】[解析] 根据本章前一部分的综述，可知偶数个奇数和是偶数。在五个选项中惟一是偶数的质数是2，若2在此集合中必有9个奇数在该集合中，其和必是一个奇数。
Questions92-93 refer to the following definition.