The correct answer is option A. CO2 traps the heat of the sun in earths atmosphere.
Carbon dioxide gas has the ability to trap the heat of the sun rays near earth's surface. This is known as green house effect. This is the reason why earth's atmosphere remains warm even in the absence of sunlight i.e. during evening and night. The heat which is trapped by CO2 persists in the environment rather than dissipating back into the space. It also means that earth would have been less warmer without an atmosphere because it is the atmosphere of earth which has CO2 and other green house gases.
