Question: Homes that are built to be environmentally friendly because they use energy more efficiently than other homes are called "green" homes. "Green" homes often have reflective roofs and walls made of recycled materials. The windows in these energy-saving homes are double-paned, meaning each window has two pieces of glass. Double-paned windows have a layer of air between the window panes. This layer is a barrier against extreme temperatures and saves energy. A solar panel on a "green" home uses

  Options: 
 A. chemical energy
 B. mechanical energy
 C. a renewable energy source
 D. a nonrenewable energy source
Answer: C