$A = \{3, 5, 7\}$, $B = \{5, 3, 3, 7\}$, $C = \{7, 7, 3, 5, 5\}$. Which is true?

Sets are defined only by their distinct members, and repeated elements do not count more than once. Since $A$, $B$, and $C$ all contain exactly the same distinct elements $3$, $5$, and $7$, they are equal.