Answer-
The first graph correctly describes the situation.
Solution-
First scenario-
As the bus gets off the freeway, that means the driver pushed the brake. That is why the speed decreases constantly to zero. So the slope is negative here.
Second scenario-
As the bus stops at the rest stop for passengers to get lunch, the vehicle is still. As the bus is in still position, so its speed is zero as long it is still at the rest stop. So the slope is zero here.
Third scenario-
As the bus now starts moving towards freeway, its speed increases constantly. So the slope is positive in this case.
