What is the difference of the polynomials?

(5x3 - 2x2 + 9x - 12) - (6x2 - 5)

a 5x^3 - 4x^2 + 9x - 7
b 5x^3 - 8x^2 + 9x - 17
c 5x^3 - 8x^2 + 9x - 7
d 5x^3 + 4x^2 + 9x - 7