Achange in the average kinetic energy of the molecules of an object may best be detected by measuring a change in the object's

mass
speed
temperature
weight

temperature

Explanation:

The temperature of an object will automatically reflect the increase or decrease in the average kinetic energy of the molecules of the object, kinetic energy is related with the movement, but when the molecules of the object are moving and reflecting kinetic energy it is not necessary the case that that would be provoqued by the movement of the object so temperature would be the best way to measure the change in the molecules kinetic energy.