The correct option is C
Both B and C
Ozone is a significant gas in the stratosphere because it absorbs the UV rays and do not allow them to reach the earth's surface. There it is formed by the reaction of oxygen with UV rays. However, tropospheric or ground-level ozone is formed as a secondary pollutant and is harmful. It acts as a major constituent of the photochemical smog. It also traps and reflect back the infra-red rays coming from the earth's surface. Here, it is formed when the primary pollutants react with the oxygen in the presence of sunlight. So, it acts as a greenhouse gas.
Hence, the correct answer is 'Both B and C'.