You are asking for the proportion of numbers 1–6 that are greater than 2. The ones greater than 2 are 3, 4, 5, 6. There are 4 of them, out of the 6 possible numbers. Since the cube is fair, all numbers have equal probability. This means the probability of an outcome greater than 2 is
... 4/6 = 2/3
The appropriat choice is ...
... C.) 2/3