Any sources related to industries that cause air pollution such as Oil refineries, cigarette companies, thermal electricity generating firms and the like.
Explanation:
A biased source in a subject usually has some sort of interest in it which is usually financial. This is why we'd expect cigarette companies to lie about the effects of smoking on the lungs.
It is the same thing here. You included no options but the biased source should be one that stands to benefit from misleading the public on the effects of air pollution on health so that people are less enraged and they can continue benefitting from their harmful activities.
