Without the provided graph, it's impossible to determine between which points a bus is moving at a constant speed. However, when a bus moves at a constant velocity, the related velocity-time graph shows a horizontal line, and acceleration is zero. The correct answer is option C.
The question asks for the selection of points between which a bus is moving at a constant speed, based on a given scenario or graph which is unfortunately not provided in the query. To answer such questions, one would typically identify the section of a velocity-time graph where the line is horizontal, indicating a steady speed. Without the graph, it isn't possible to provide a definitive answer. However, for conceptual understanding, in scenarios where acceleration is zero, a velocity-time graph would show a constant velocity.
Moreover, if the bus travels at a constant velocity of 12 m/s for 6 seconds, the displacement-time graph would show a straight line with a slope of 12, the velocity-time graph would show a horizontal line at 12 m/s, and the acceleration-time graph would be a horizontal line at 0 m/s2, indicating no acceleration.
When a bus accelerates from rest at 2 m/s2 until it reaches 20 m/s and then travels at this constant speed, the velocity-time graph would initially slope upwards till it reaches 20 m/s then becomes a horizontal line. When decelerating uniformly to a stop over 5 seconds, the graph would show a downward slope returning to 0 m/s.
Therefore, option C is correct.