The zeroes of the function f(x)=x2−ax+2a are integers. What is the sum of all possible values of a?<spanclass=′latex−bold′>(A)</span>7<spanclass=′latex−bold′>(B)</span>8<spanclass=′latex−bold′>(C)</span>16<spanclass=′latex−bold′>(D)</span>17<spanclass=′latex−bold′>(E)</span>18