A distance-time graph for a motorcyclist that forms a straight, sloped line indicates that the motorcyclist is moving at a constant speed. This is because the distance covered increases uniformly with time, meaning there is no change in speed over time. The steeper the slope of the line, the higher the speed of the motorcyclist. If the graph were curved, it would indicate changing speed. For a velocity-time graph corresponding to constant speed, the graph would be a horizontal line, representing a constant velocity throughout the motion, with no acceleration.