challenge: What is the primary mission of the Joint Center for Artificial Photosynthesis (JCAP)?
  
  A. To create a new source of renewable energy using wind power
  B. To improve the efficiency of fossil fuel-based power plants
  C. To develop a cost-effective method for producing solar panels
  D. To find a cost-effective method to produce fuels using only sunlight, water, and carbon-dioxide
  Answer: 