replacing wood doors with aluminum doors using more insulation in the walls of the home removing thick rugs and heavy curtains in the home painting the roof of the home white to reflect light
I gave my students this multiple choice question: Which of the following could help to reduce a home heating bill in winter?

Only one answer is correct among these 4 choices:
- replacing wood doors with aluminum doors
- using more insulation in the walls of the home
- removing thick rugs and heavy curtains in the home
- painting the roof of the home white to reflect light

Could you tell me which one is correct?

using more insulation in the walls of the home