Explanation:
We simply list each possible choice in the form (x,y) where x is the result of the first die and y is the result of the second die.
The sum must be 8 so x+y = 8.
Choice A is the complete list showing all possible sums of 8.
Choice B is missing (5,3) and (6,2).
Choice C is missing (4,4)
Choice D shows (1,7), but 7 isn't a valid roll of a six-sided die.