Determine whether 25a^2 − 49b^6 is a difference of two squares. If so, factor it. If not, explain why.
A. It is not a difference of squares because −49b^6 is not a perfect square.
B.(5a + 7b^3)(5a − 7b^3)
C.(5a − 7b^3)(5a − 7b^3)
D.(5a − 7b^6)(5a + 7b^6)