If the coefficients of x³ and x⁴ in the expansion of (1+ax+bx²)(1−2x)¹⁸ in powers of x are both zero, the (a, b) is equal to
(1) (16,251/3)
(2) (14,272/3)
(3) (14,251/3)
(4) (16,272/3)