Even though the costs of paying baseball players amounts to a sum greater than one half of the overall cost of operating a Major League Baseball team last year, Major League Baseball franchise owners were still willing to pay increasingly higher salaries to top players.
amounts to a sum greater
amounts to more
amounted to more
amounted to a greater sum
amounted to greater
I have no idea how can C be correct because cost is uncountable and should be compared by using greater....