Smoke emerging from a campfire at the bottom of a hill is being observed by a person at some distance, as shown in the figure. It is evening and the sun has just set behind the hill. Consider regions I and II of the smoke going up the sky

• A. region I will be slightly brighter than the hill and region II will be slightly brighter than the sky
• B. region I will be slightly darker than the hill and region II will be slightly brighter than the sky
• C. region I will be slightly brighter than the hill and region II will be slightly darker than the sky
• D. region I will be slightly darker than the hill and region II will be slightly darker than the sky