Explanation
Without the greenhouse effect, the average temperature of the Earth would be below 0 degrees Celsius (option C). The greenhouse effect is a natural process that occurs when certain gases in the Earth's atmosphere, such as carbon dioxide and methane, trap heat from the sun and prevent it from escaping into space. This process helps to maintain a relatively stable and habitable temperature range on Earth.
If the greenhouse effect did not exist, the Earth would lose a significant amount of heat, resulting in a much colder average temperature. This is because the greenhouse gases act as a thermal blanket, trapping heat and preventing it from dissipating rapidly. Without this warming effect, the Earth's surface temperature would be significantly lower, making it difficult for life as we know it to exist.