Final answer:
During the time interval labeled "b", the object was at rest.
Step-by-step explanation:
During the time interval labeled "b", the object was at rest. This can be determined by considering the information provided that the object is either at rest or it returns to the initial position.
In this case, since the object starts from rest and there is no information indicating a change in its position or velocity, we can conclude that it remains at rest throughout the time interval labeled "b".