The greenhouse effect occurs when our planet's atmosphere is overheated by the arriving sun rays that get trapped in the large amount of air pollutants, such as carbon dioxide, methane, but also water in form of steam. This is mainly caused by anthropic contamination, such as the combustion of fossil fuels.
We can say then that the correct answer is the last one: D. Light is trapped on Earth and cannot escape to space. The CO2 molecules, and the other ones, absorb the temperature from the sun and make the surrounding air to warm up too.