Concept:The crow-flies distance is the shortest straight-line distance between two points on a map, measured with a ruler and converted using the map scale.Explanation:Locate Obasa and Oju on the map.Measure the straight line between the two places using a ruler or a piece of paper.Apply the given map scale to convert the measured length into real ground distance.The measured straight-line distance corresponds to approximately 20km on the ground.Answer:C. 20km
