What is the completely factored form of this polynomial?
5x4 + 20x3 - 105x2
OA. 5x2(x+3)(x - 7)
B.
5x2(x + 3)(x - 7)
OC. 5x2(x - 3)(x + 7)
OD. 5x3(x - 3)(x + 7)