What is the completely factored form of this polynomial?
$5 x^4+20 x^3-105 x^2$
A$5 x^2(x-3)(x+7)$
B$5 x^2(x+3)(x-7)$
C$5 x^3(x+3)(x-7)$
D$5 x^3(x-3)(x+7)$
$5 x^4+20 x^3-105 x^2$
A$5 x^2(x-3)(x+7)$
B$5 x^2(x+3)(x-7)$
C$5 x^3(x+3)(x-7)$
D$5 x^3(x-3)(x+7)$