Suppose that S is a subset of {1,2,3,...,25} such that the sum of any two (not necessarily distinct) elements of S is never an element of S. What is the maximum number of elements S may contain?<spanclass=′latex−bold′>(A)</span>12<spanclass=′latex−bold′>(B)</span>13<spanclass=′latex−bold′>(C)</span>14<spanclass=′latex−bold′>(D)</span>15<spanclass=′latex−bold′>(E)</span>16