Question

Can anyone help me answer this question?
Let A, B, C e sets. Which of the following properties is the cumulative law?
a. A ∪ B = B ∪ A
b. A ∩ B = B ∩ A
c. A ∩ B = B ∪ A
d. (A ∪ B) ∪ C = A ∪ (B ∪ C)