Each of the 39 students in the eighth grade at Lincoln Middle School has one dog or one cat or both a dog and a cat. Twenty students have a dog and 26 students have a cat. How many students have both a dog and a cat?<spanclass=′latex−bold′>(A)</span>7<spanclass=′latex−bold′>(B)</span>13<spanclass=′latex−bold′>(C)</span>19<spanclass=′latex−bold′>(D)</span>39<spanclass=′latex−bold′>(E)</span>46