If A = {a, b, c, d} and B = {c, d, e, f}, what is A ∩ B?
Answer: C
The intersection of two sets, denoted by A ∩ B, is the set of all elements that are common to both A and B.
A = {a, b, c, d}
B = {c, d, e, f}
A ∩ B = {c, d}