A、30%. B、50%. C、70%. D、60%. A原义再现。从文中可知，太阳照射的能量有30%被反射回了太空。

Global warming is caused by an increase in the greenhouse effect. The greenhouse effect is not a bad thing by itself--it’s what allows Earth to stay warm enough for life to survive.
    You can think of the Earth sort of like your car sitting out in a parking lot on a sunny day.  You’ve probably noticed that your car is always much hotter inside than the outside temperature if it’s been sitting there for a while. The sun’s rays enter through your car’s windows. Some of the heat from the sun is absorbed by the seats, the dashboard and the carpeting and floor mats. When those objects release this heat, it doesn’t all get out through the windows. So a certain amount of energy is going in, and less energy is going out.  The result is a gradual increase in the temperature inside your car.
    When the sun’s rays hit the Earth’s atmosphere and the surface of the Earth, approximately 70 percent of the energy stays on the planet, absorbed by land, oceans, plants and other things.  The other 30 percent is reflected into space by clouds, snow fields and other reflective surfaces. But even the 70 percent that gets through doesn’t stay on earth forever. The things around the planet that absorb the sun’s heat eventually radiate that heat back out. Some of it makes it into space, and the rest of it ends up getting reflected back down to earth when it hits certain things in the atmosphere, such as carbon dioxide, methane gas and water vapor. The heat that doesn’t make it out through Earth’s atmosphere keeps the planet warmer than it is in outer space, because more energy is coming in through the atmosphere than is going out. This is all part of the greenhouse effect that keeps the Earth warm.