The greenhouse effect refers to the fact that the atmosphere helps to maintain the temperature on Earth by preventing the heat from the sunlight to escape into space.
Greenhouse gases are the ones that are capable of preventing the sun's heat from escaping, such as:
• carbon dioxide
,
• methane
,
• ozone
,
• water vapor
The greenhouse effect is not a harmful process just by itself, in fact, it allows the existence of life on Earth, but the human activity adds greenhouse gases to the atmosphere, causing more heat to be retained.
This means the right answer is A, Gases such as carbon dioxide and methane reflect heat from the Earth back towards Earth’s surface.