A. greater
The slope of a speed graph represents the rate of change of speed over time, which is equivalent to the acceleration. A steeper slope means a greater change in speed over time, indicating a higher acceleration. Since the average speed is calculated by dividing the total distance traveled by the total time taken, a greater acceleration means covering a larger distance in the same amount of time, resulting in a higher average speed. Therefore, the greater the slope of the line of a speed graph, the greater the average speed.