Answer:
A. gas molecules having three or more atoms
Step-by-step explanation:
A greenhouse gas has the property to absorb infrared radiation and radiating it back to the earth surface.
A greenhouse gas must have three atoms or more, that will help the gas to absorb infrared radiation and restricts its way out of the atmosphere. some example of greenhouse gases are methane (CH4), carbon-dioxide (CO2) and nitrogen oxide (NO2).
Hence, the correct answer is "A".