If r is positive and the line whose equation is x+y=r is tangen to the circle whose equation is x2+y2=r, then r equals<spanclass=′latex−bold′>(A)</span>21<spanclass=′latex−bold′>(B)</span>1<spanclass=′latex−bold′>(C)</span>2<spanclass=′latex−bold′>(D)</span>2<spanclass=′latex−bold′>(E)</span>22