The given sum is -8 + 17.
The second expression 17 + (-8) is equivalent to 17 - 8, and also it's equivalent to -8 + 17. B is correct.
The third expression is -8 + 8 + 9 which is equivalent to -8 + 17 because 8 + 9 = 17. C is correct.
Therefore, the right answers are B and C.