The height and radius of the cone of which the frustum is a part are h1 units and r1 units respectively. Height of the frustum is h2 units and the radius of the smaller base is r2 units. If h2 : h1 = 1 : 2 then r2 : r1 is
(1) 1 : 3
(2) 1 : 2
(3) 2 : 1
(4) 3 : 1