By saying "It's a two-horse race" (Line 6, Para. 4), the author indicates that
A.the principals of those two schemes mentioned above are competing with each other B.there are mainly two retailers of personal tax software in the present market C.Intuit's Turbo Tax and H&R Block's Taxlut are the names of two horses known by everyone D.those smaller retailers will be merged into the bigger ones in the nearest future