Let a, b, and c be three distinct one-digit numbers. What is the maximum value of the sum of the roots of the equation (x−a)(x−b)+(x−b)(x−c)=0?
<spanclass=′latex−bold′>(A)</span>15<spanclass=′latex−bold′>(B)</span>15.5<spanclass=′latex−bold′>(C)</span>16<spanclass=′latex−bold′>(D)</span>16.5<spanclass=′latex−bold′>(E)</span>17