Let x = a + bi and y = c + di and z = f + gi
which statements are true? theres multiple answers

a. x + y = y + x

b. (x × y) × z = x × (y × z)

c. x – y = y – x

d. (x + y) + z = x + (y + z)

e. (x – y) – z = x – (y – z)

True statements:
a) x + y = y + x  ⇒ commutative property of addition
b) (x * y) * z = x * (y * z) ⇒ associative property of multiplication
d) (x + y) + z = x + (y + z) ⇒ associative property of addition

False statements:
c) x - y = y - x  should be: x - y = - y + x
e) (x - y) - z = x - (y - z) should be: (x - y) - z = x - (y + z)

What mathematical statement is missing ? ? the answer is b