Pressure P is given by P = a-x²/bt, where x is distance and t is time, the dimensions of a and b are

(a) M⁰ L² T0 , M¹ L³ T¹
(b) M⁻¹ L² T0 , M¹ L⁻³ T¹
(c) M0 L² T0 , M⁻¹ L³ T¹
(d) M0 L² T0 , M1 L² T