The correct answer is B. I, II, and IV only.
Here's a breakdown of each statement:
I. It is a natural process - True. The greenhouse effect is indeed a natural process essential for life on Earth, as it helps maintain the planet's temperature.
II. It helps to filter harmful radiation from the sun - True. The greenhouse gases, while primarily responsible for the greenhouse effect, also contribute to filtering certain harmful radiation from the sun.
III. It is caused by gases like chlorofluorocarbons - False. While chlorofluorocarbons (CFCs) are greenhouse gases that contribute to ozone depletion and have a greenhouse effect, they are not a primary cause of the natural greenhouse effect, which is mainly due to gases like carbon dioxide, methane, and water vapor.
IV. Some human activities enhance the greenhouse effect - True. Human activities, such as burning fossil fuels and deforestation, release additional greenhouse gases, enhancing the greenhouse effect and contributing to climate change.
Thus, only statements I, II, and IV are true.