Four friends start together from the same point and stop after 20s. Their motions are as follows:
P: walks straight 40m east.
Q: walks 25m east, then 15m west.
R: runs along a semicircular track of radius 10m to the opposite end.
S: completes one full circular lap of radius 10m.
Arrange them in descending order of the magnitude of their average velocities.
a) S > P > Q > R
b) Q > P > R > S
c) P > R > Q > S
d) P > Q > R > S