Final answer:
The key to understanding the greenhouse effect is greenhouse gas concentrations, as they trap heat in the atmosphere.
Step-by-step explanation:
The key to understanding how the greenhouse effect works is recognizing the role of greenhouse gas concentrations. These gases, including carbon dioxide, methane, and nitrous oxide, act like the glass of a greenhouse by allowing sunlight to enter the atmosphere and preventing the heat from escaping into space.
Thus, the correct answer to the question is c) Greenhouse gas concentrations.
These gases absorb infrared radiation from the sun, which heats the earth's surface. Since the Industrial Revolution, human activities such as the burning of fossil fuels and deforestation have significantly increased these gas concentrations, leading to a strengthened greenhouse effect and global warming.