A train moves along a straight north–south track in three consecutive stages without changing the magnitude of its speed in each moving stage. It first travels northward for a certain time, then remains stationary for an interval, and finally travels southward for the same duration as the first stage before coming to rest.
(i) Without performing any numerical calculation, state whether the average speed for the complete journey is zero or non-zero. Give reasons.
(ii) For each of the following possible final positions of the train, decide whether the average velocity over the whole journey is positive (northward), negative (southward), or zero. Justify your answers in each case.
(A) The train stops at a point north of the starting station.
(B) The train stops exactly at the starting station.
(C) The train stops at a point south of the starting station.