What can you say about the motion of a body if its displacement$-$time graph is a straight line parallel to the time axis ?

What does the slope of a displacement$-$time graph represent ? Can displacement$-$time sketch be parallel to the displacement axis ? Give reason to your answer.

The velocity$-$time graph of a body has a negative slope. The body is undergoing

A body can have zero average velocity but not zero average speed. Justify giving an example.

Four speed$-$time graphs are shown below

Which graph represents the following case ?

$(i)$ A ball thrown vertically upwards and returning to the hand of the thrower ?

$(ii)$ A body decelerating to a constant speed and then accelerating.