Answer: Some part of solar energy is absorbed by the land and ocean, resulting in the heating of the earth. The rest of the energy is reflected back to space. The energy radiated from earth is trapped by greenhouse gases and makes the earth warm. Some undesirable human activities, such as the burning of fossil fuels and deforestation release more greenhouse gases into the atmosphere. More greenhouse gases cause more trapping of solar energy and global warming. Thus, Option C is the correct answer.