For events A and B with probabilities P(A)=p, P(B)=q(0<p,q<1), suppose
P(A∪B)=p+q−2pq.
Which of the following describes their independence?
a) They are independent only when p=q.
b) They are never independent for 0<p,q<1.
c) They are independent for all p and q.
d) They are independent only when p=0 \text{ or } q=0$.