Pairwise but Not Mutual Independence

Let the sample space be $\Omega = \{1, 2, 3, 4\}$ with uniform probability $P(\{i\}) = 1/4$. Define $A = \{1, 2\}$, $B = \{1, 3\}$, $C = \{1, 4\}$. Show that $A$, $B$, $C$ are pairwise independent but not mutually independent.