<http://schema.org/description>
"You have your wheelbarrow, concrete mixer and shovel all ready. But the hard part of making concrete, even with the best of tools, is getting the mixture right. Concrete has been used for centuries, but the concrete mixtures used today have come a long way from the mud mixtures that were once used. Take this quiz to see what you know about how concrete is made."^^<http://www.w3.org/2001/XMLSchema#string>
<http://home.howstuffworks.com/home-improvement/construction/materials/concrete-quiz2.htm>