Earth Day: How much do you know about climate change? Take our quiz.

A lot of people have opinions about climate change, but do they really know what they are talking about? Test your knowledge with this quiz.

9. What energy source is the single largest contributor of human-made carbon dioxide in our atmosphere?

NASA/Reuters/File
A full moon appears through the blue glow of the Earth's atmosphere, in this photo taken aboard the Space Shuttle Discovery in 1999.

Natural gas (methane)

Coal

Petroleum

Nuclear power

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