Test your brainpower

What is the most common fuel for making electricity in the United States?

Answer:

Coal is the most common fuel. Burning coal produces 50% of the electric power in the United States.

One day's worth of sunlight, however, could provide enough energy for the Earth's 6 billion people for 27 years, with a lot less mess. Scientists and engineers are working to develop cheaper, more practical ways to turn sunlight into energy.