A 1500 kg car is traveling along a straight road at a speed of 20 m/s. Two seconds later, its speed is 21 m/s. Assuming constant acceleration in this time interval, what is the car's acceleration?
(a) 0.5 m/s²
(b) 0.25 m/s²
(c) 0.75 m/s²
(d) 1 m/s²