What is true, best tries to resolve the paradox in the above argument?

The average effect on mortality in a large group of people may mask an effect of vitamin e on the lifespan.-ans: (a) (this is a resolve the paradox type question. the option which fills up the gap in the argument, is the correct one. here both the statements are contradictory, so the correct option should remove this contradiction. (a) is correct because it says that in a large group, the effect on a small group may be averaged out. (b) talks about age, which is not an issue. (c) suggests some solution but does not resolve the paradox. (d) talks about a different group which is not in question. (e) is also not relevant because it is already mentioned that the samples were large and were random, so no question of not including any particular group arises.)