Which of these is always true for any set AAA?
A∪Ac=∅A \cup A^c = \emptysetA∪Ac=∅
A∩Ac=∅A \cap A^c = \emptysetA∩Ac=∅
A∩Ac=UA \cap A^c = UA∩Ac=U
A∪Ac=AA \cup A^c = AA∪Ac=A