A portfolio is considered 'dominated' if

A portfolio is considered dominated when it is not on the efficient frontier, which is another way of saying that there exists another portfolio with a better risk reward payoff. Therefore Choice 'a' is the correct answer.If the portfolio has a higher mean and the same or lower standard deviation than any other portfolio, this means it is already on the efficient frontier and is not dominated. The other choices do not make any sense in the context of the question.