A. On top of all this, cities contain millions of people, who constantly generate heat by using machines and participating in other activities.

Question: "(10) On top of all this, cities contain millions of people, who constantly generate heat by using machines and participate in other activities." What revision should be made in sentence 10? A.On top of all this, cities contain millions of people, who constantly generate heat by using machines and participating in other activities. B.On top of all this, constantly generating heat by using machines and participating in other activities are cities, which contain millions of people. C.On top of all this are cities that contain millions of people, and they constantly generate heat, use machines, and participate in other activities. D.On top of all this, cities contain millions of people, and the people constantly generate heat by using machines and also by participation in other activities.