If x and y are prime numbers, which of the following CANNOT be the sum of x and y?	Select:  A) 5  B) 9  C) 13  D) 16  E) 23
All answer choices but D are odd. In order odd number to be the sum of two prime numbers one must be even, so 2, and another odd.   Now, 23=2+21. Since 21 is not a prime then 23 cannot be written as the sum of two prime numbers.   Answer: 23.
<result>E</result>
If x and y are prime numbers, which of the following CANNOT be the sum of x and y?