Photo quiz: Gear for green buildings

The answer to the previous question is B, a vertical-axis wind turbine capable of generating 1 kilowatt of electricity. A larger version of the same design is installed on Esther's Island near Nantucket.

Next question: This heliostat from Practical Solar is used to:

A. bring sunlight into buildings to cut lighting costs.

B. convert sunlight into electricity.

Answer and new question on next page.

Photo by Martin LaMonica/CNET

Caption by Martin LaMonica