a is the sum of x consecutive positive integers. b is the sum of y consecutive positive integers. For which of the following values of x and y is it impossible that a = b?
(A) x = 2; y = 6
(B) x = 3; y = 6
(C) x = 7; y = 9
(D) x = 10; y = 4
(E) x = 10; y = 7
정답은 d번이라고 하는데요.. 문제가 이해가 안되요 ㅠㅠ 설명 좀 부탁드려요.ㅠㅠ