C

We’re told there were 50 sterilzations of a “*set* of nylon instruments” and 50 sterilzations of a “*set* of stainless steel instruments.” But we have no idea how many instruments are in a “set” of either. There could 10 nylon instruments in a set and only 5 stainless steel instruments in a set. In that case, (C) could be true. I know, this is an annoying, picayune detail the question expects you to notice. But, there’s a lesson about careful reading here!