If x and y are different integers, both divisible by 9, then which is not necessarily true?
Choose the correct choice from the following:
A) x^2 + y^2 is divisible by 9	B) x - y is divisible by 9	C) xy is divisible by 9	D) x + y is divisible by 9	E) x + y is divisible by 18
Let x = 9k and let y = 9j.   Then x+y = 9(k+j) and k+j could be even or odd.   Thus 9(k+j) is not necessarily divisible by 18.   The answer is x + y is divisible by 18.
<result>E</result>
If x and y are different integers, both divisible by 9, then which is not necessarily true?