Final answer:
The 2008 event associated with the clean air's important placemark was the Beijing Olympics.
Step-by-step explanation:
The 2008 event associated with the clean air's important placemark was the A. Beijing Olympics. China's fast-growing economy and burgeoning industry have translated into notoriously poor air quality, with smog hanging heavily over major cities like Beijing. The Beijing Olympics brought attention to the issue of air pollution and the need for environmental protection.