Choose the conditional statement that can be used with its converse to form the following biconditional statement: "a triangle is equilateral if and only if its three angles are congruent." a. if an equilateral triangle has three congruent angles, then it is equilateral. b. if a triangle has three congruent angles, then it is not equilateral. c. if the three angles of a triangle are not congruent, then the triangle is not equilateral. d. if a triangle is equilateral, then its three angles are congruent.