Answer: Oxygen (I don’t see the options)
Explanation: A greenhouse gas is a gas that produces heat as it builds up in the atmosphere. It also becomes trapped in the atmosphere, so it cannot escape the inner layers of Earth's atmosphere. As a result, these gases cause pollution because they dirty up the atmosphere.
Carbon dioxide is a main greenhouse gas, found in car exhaust pipes.
Methane and nitrous oxide is another type of greenhouse gas.
*Oxygen is the only clean gas out there because we need it to survive. Therefore, the only gas that is not a greenhouse gas*