Consider the following statements regarding Ozone: I. Ozone contributes to 3-7% of Greenhouse effect II. The largest net source of tropospheric ozone is influx from the stratosphere III. Large amounts of ozone are also produced in the troposphere by photochemical reactions, the amounts increasing with high levels of air pollution.

• A.  I & II                           
• B.  II & III
• C.  Only III           
• D.  All the above