Before tackling the statement, simplify the complex expression in the question stem:
a2 − b2 = a2 − ab
-b2 = -ab
0 = b2 − ab
0 = b(b − a)
So either b or (b − a) = 0, but since b ≠ a, (b − a) ≠ 0.
b = 0, so we look for a statment that connects c to b.
This statement connects c to a, which we know nothing about. It`s insufficient; the answer must be B, C, or E.
This statement does exactly what we want. c3 = 0 = c, so we can answer the question. This statement is sufficient.
The correct answer is B.