Actually we have the given problem which is more harder than the problem which I m mentioning below..
Let M denotes Turing machines that accepts exactly 3 strings..So this problem is not even RE as by the technique known as dovetailing also which is used for enumeration process effectively , we are not able to confirm which 3 will be the part of the language as all others need to be rejected..
Hence the given problem is even harder than the problem that language accepts a finite number(say 3) of strings..
Hence it is non RE set and hence not even partially decidable.
Hence C) is the correct answer..