Explanation:

The average speed of a train is the total distance covered by the train divided by the total time taken to cover that distance. It is a measure of how fast the train is traveling over a particular distance. The average speed of a train is independent of the following factors:

A) The duration of the stops: The duration of stops made by a train during its journey does not affect its average speed. This is because the total distance covered by the train during the journey remains the same irrespective of the duration of the stops. For example, if a train covers a distance of 100 km in 2 hours and makes a stop of 30 minutes, the total time taken for the journey would be 2 hours and 30 minutes. However, the total distance covered by the train would remain 100 km. Therefore, the duration of stops does not affect the average speed of a train.

B) The acceleration and braking retardation: The acceleration and braking retardation of a train refer to the rate at which the train speeds up and slows down, respectively. These factors do affect the total time taken by the train to cover a particular distance. However, they do not affect the average speed of the train because the total distance covered by the train remains the same. For example, if a train covers a distance of 100 km with an average speed of 50 km/h, it would take 2 hours to complete the journey. However, if the train accelerates and decelerates during the journey, the total time taken to cover the same distance may increase, but the average speed of the train would remain the same.

C) The distance between stops: The distance between stops does affect the total time taken by the train to complete the journey. However, it does not affect the average speed of the train because the total distance covered by the train remains the same. For example, if a train covers a distance of 100 km with an average speed of 50 km/h and makes a stop every 10 km, it would take longer to complete the journey than if it made a stop every 20 km. However, the average speed of the train would remain the same in both cases.

D) The running time: The running time of a train refers to the time taken by the train to cover a particular distance without making any stops. This factor does affect the average speed of the train because the total distance covered by the train and the time taken to cover that distance are both affected. For example, if a train covers a distance of 100 km in 2 hours without making any stops, its average speed would be 50 km/h. However, if the same train covers the same distance in 2 hours and 30 minutes without making any stops, its average speed would be 40 km/h.