[university stats] set theory

this is the problem: For each of the following statements, decide whether they are always true (i.e., true for all sets A, B, C) or not. If they are not always true, provide a counter example for instance in the form of a Venn Diagram or by listing specific sets. the one that i m stuck on is : If A ∪ B = C and A ∩ C = ∅, then A = ∅.