Paheli moves on a straight road from point A to point C. She takes 20 minutes to cover a certain distance AB and 30 minutes to cover the rest of distance BC. She then turns back and takes 30 minutes to cover the distance CB and 20 minutes to cover the rest of the distance to her starting point. She makes 5 rounds on the road the same way. Paheli concludes that her motion is
(a) only rectilinear motion.
(b) only periodic motion.
(c) rectilinear and periodic both.
(d) neither rectilinear nor periodic.
