The answer is C.
Even and odd numbers are able to be rolled on a number cube. 1, 3, and 5 are the odd numbers and 2, 4, and 6 are the even numbers. This rules out A.
Factors of 6 are able to be rolled on a number cube. The factors of 6 are 1, 2, 3, and 6. This rules of B.
This leaves the answer C. There are no numbers less than 1 on a number cube, so rolling it would be impossible.