Concept:The map scale shows that 1 cm on the map equals 0.5 km on the ground.Explanation:Measure the straight-line distance between Doba and Sasi on the map.The measured crowfly distance is about 11 cm.Using the scale 1:50,000, we have 1 cm=0.5 km.Actual distance =11×0.5=5.5 km.Answer:C. 5.5 km