Use three levels of $4\times 1$ MUXs. $16$ in first level controlled by $EF$ to receive $64$ inputs and generate $16$ outputs, $4$ in $2$nd level controlled by $CD$ to receive $16$ outputs from first level and generate $4$ outputs, and one in last level controlled by $AB$ to select one of the four outputs from the $2$nd level as the final output.
So, $X_{1} Y_{1} \equiv E F ; X_{2} Y_{2} \equiv C D ; X_{3} Y_{3} \equiv A B$
Hence, answer is Option C.
NOTE : A common mistake student might do is that they might assign $AB$ to the select lines of first level. This will not give desried behavious of Mux.
