The correct response is:
It allows the atmosphere to retain heat.
The greenhouse effect is a natural process that warms the Earth's surface. When the Sun's energy reaches the Earth, some of it is reflected back to space and the rest is absorbed, warming the planet. The Earth then emits this energy in the form of infrared radiation. Greenhouse gases in the atmosphere trap some of this heat and prevent it from escaping back into space, which helps to keep the planet warm enough to support life.