What are the vertical and horizontal asymptotes for the function f(x)= x^2+x-6/x^3-1?

a) vertical asymptote: x = 1
horizontal asymptote: none

b) vertical asymptote: x = 1
horizontal asymptote: y = 0

c) vertical asymptote: x = –2, x = 3
horizontal asymptote: y = 0

d) vertical asymptote: x = –2, x = –3
horizontal asymptote: none