See that we are not making any multiplications, so the commutative property of multiplication and associative property of multiplication are not the correct answers.
Thus we have now the associative property of addition and commutative property of addition. What do they say?
Associative property of addition: Changing the position of the parenthesis does not affect the value of the sum.
Commutative property of addition: Changing the order of the numbers, the sum is not modified.
See that what is being demonstrated is that the position of the parenthesis does not affect the result, so the right answer is letter A, Associative property of addition!