pls explain

Consider a two-objective optimization problem in which we want to maximize f1(x) and minimize f2(x). Suppose the problem has a square criterion/objective space with y1E [0,1] and y2E [0,1], i.e. y1 takes any value from 0 to 1 and y2 takes any value from 0 to 1. Which point(s) is (are) Pareto- optimal? O (0,0) O (1,0) O (1, 1) O (0,0), (1,0) and (1, 1)