For function f(x), which pair of limits would verify the existence of a vertical asymptote at x = -1?
a. lim f(x) = [infinity] and lim f(x) = [infinity]
x→ -1⁻ x→ -1⁺
b. lim f(x) = -1 and lim f(x) = -1
x→ -[infinity] x→ [infinity]
c. lim f(x) = c and lim f(x) = c for some value c
x→ -1⁻ x→ -1⁺
d. lim f(x) = -1 and lim f(x) = -1 for some value c
x→ c⁻ x→ c⁺
