Select the function whose end behavior is described by f(x) → [infinity] as x → [infinity] and f(x) → -[infinity] as x → -[infinity].
a) f(x) = 7x⁹ - 3x² - 6
b) f(x) = 2x³ + 5x² - 4
c) f(x) = 4x⁴ - 2x² + 3
d) f(x) = -6x⁵ + 8x² + 1