For each of the following four ordered pairs, the first value represents a possible distance travelled in one trip and the second value represents a possible magnitude of displacement for the same trip. Analyse each pair and state with proper reasoning whether it is physically possible or impossible.
(a) (250m,250m)
(b) (400m,500m)
(c) (600m,0m)
(d) (1.2km,0.8km)
For every part, clearly justify your answer in two or three sentences, referring to the fundamental relation between distance and displacement wherever relevant.