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--Choose one-- A. It causes cancer and mutations in living things. B. It removes carbon dioxide from our atmosphere. C. It slows down Earth's liquid outer core.

--Choose one-- A. Water vapor clouds in the atmosphere. B. A thick atmosphere and a magnetic field. C. Greenhouse gases, like carbon dioxide.

--Choose one-- A. Volcanic activity would increase and     Earth would become very hot. B. Carbon dioxide would not be released into the     atmosphere and Earth would become very cold. C. Space radiation would bombard Earth's surface     and harm life.

--Choose one-- A. Volcanic activity would increase. B. Carbon dioxide would not be released     into the atmosphere. C. Space radiation would bombard Earth's surface.