Concept:Map scale shows the relationship between a map measurement and the actual ground distance.Explanation:The scale is 2 cm on the map = 1 km on the ground.The distance between the towns on the map is 20 cm.Find how many scale units fit into the map distance: 2 cm20 cm=10.Multiply this by the ground distance per unit: 10×1 km=10 km.Answer:C. 10 km