Four students take an exam. Three of their scores are 70,80, and 90. If the average of their four scores is 70, then what is the remaining score?<spanclass=′latex−bold′>(A)</span>40<spanclass=′latex−bold′>(B)</span>50<spanclass=′latex−bold′>(C)</span>55<spanclass=′latex−bold′>(D)</span>60<spanclass=′latex−bold′>(E)</span>70