8 is the cube of integer 2 but is not the square of any integer. 
9 is the square of integer 3 but in not the cube of any integer.
36 is the square of integer 6 but in not the cube of any integer.
64 is both the square of integer 8 and also the cube of integer 4.

So the answer, if listed, must be d).

But that does not rule out the possibility that 64 is the smallest
such integer, and the smallest one was omitted. (I have seen multiple
choice tests which the test-maker erroneously listed only false choices!

16, 25, 49 are the only perfect squares > 1 not listed and 27 is the only
perfect cube > 1 not listed.  But the same could be said about these as
about the incorrect choices listed, so 64 is the smallest such integer.  

Edwin