Let a<b<c<d be integers. If one of the roots of the equation (x−a)(x−b)(x−c)(x−d)−9 is x=7, what is a+b+c+d?<spanclass=′latex−bold′>(A)</span>14<spanclass=′latex−bold′>(B)</span>21<spanclass=′latex−bold′>(C)</span>28<spanclass=′latex−bold′>(D)</span>42<spanclass=′latex−bold′>(E)</span>63