If the line y=mx+1 intersects the ellipse x2+4y2=1 exactly once, then the value of m2 is<spanclass=′latex−bold′>(A)</span>21<spanclass=′latex−bold′>(B)</span>32<spanclass=′latex−bold′>(C)</span>43<spanclass=′latex−bold′>(D)</span>54<spanclass=′latex−bold′>(E)</span>65