According to paragraph 2, what is one reason for thinking that at one time, there were significant amounts of water on Venus? A. Because of Venus' size and mass, its volcanoes probably produced much more water vapor than volcanoes on Earth did. B. The low temperature of Venus' early atmosphere can be explained only by the presence of water. C. The presence of carbon dioxide in a planet's atmosphere is an indicator of water on that planet. D. Venus probably was struck by roughly as many comets as Earth was.