Answer:
B
Step-by-step explanation:
A is missing a combination AR and has repeats such as AG and GA. Since the order of the sides doesn't matter, AG and GA are the same thing.
C is missing many combinations, it only has 4
D has two of the same sides. The question states "you can choose two different sides" so something like AA is not an option
We can use the process of elimination to conclude the answer is B.