A 3x7 rectangle is tiled with 1x4,2x2, and 1x1 tiles. What is the least amount of 1x1’s that can be used?<spanclass=′latex−bold′>(A)</span>1<spanclass=′latex−bold′>(B)</span>2<spanclass=′latex−bold′>(C)</span>3<spanclass=′latex−bold′>(D)</span>4<spanclass=′latex−bold′>(E)</span>5