A car starts from rest, accelerates uniformly to 20 m/s in 5 s, moves with this constant speed for the next 4 s, and finally comes to rest uniformly in 3 s.
Taking the three successive intervals as I, II and III respectively, which option correctly states the sign of acceleration in each interval?
a) I: positive, II: positive, III: negative
b) I: zero, II: positive, III: negative
c) I: positive, II: zero, III: negative
d) I: negative, II: zero, III: negative