$ad'$ [fill minterm in K-map in front for $a$ and $d'$ ]
Similarly, fill all minterms for $ad'+a'c' +bc'd$, resulting K-map will be:
Option (a) $c'd'+ ad' + abc' + a'c'd$
is equivalent to given expression
Option (b) $a'c' + c'd' + ad' + abc'd$
is equivalent to given expression.
Option (c) $a'c' + ad' + abc' + c'd$
is not equivalent to given expression.
Option (d) $b'c'd' + acd' + a'c' + abc'$
is equivalent to given expression.
So, answer is C.