] Circle the statements below that are true for all values of x, y, and z. For any statement that is not always true, give an example of values of x, y, and z for which the statement is not true. (a) x(yz) = (xy)z. (b) x ÷ (y ÷ z) = (x ÷ y) ÷ z. (c) x + (y + z) = (x + y) + z. (d) x − (y − z) = (x − y) − z.