Final answer:
The greenhouse effect maintains the temperature on Earth.
Step-by-step explanation:
The correct answer is d. Greenhouse effect. The relatively constant temperature of the Earth is a result of the energy balance between the incoming solar radiation and the energy radiated from the Earth. Most of the infrared radiation emitted from the Earth is absorbed by greenhouse gases like carbon dioxide (CO₂) and water vapor (H₂O) in the atmosphere and then re-radiated back to Earth or into outer space. This radiation back to Earth is known as the greenhouse effect, and it maintains the surface temperature of the Earth about 40°C higher than it would be if there is no absorption.