Which pollutant would probably not directly harm most plants, despite having a negative impact on human populations and the environment?
a) motor oil from automobile runoff
b) acid rain from smoke stack emissions
c) carbon dioxide from automobile exhaust
d) salt pollution from fertilizers and erosion

The correct option is C. Carbon dioxide from automobile exhaust

Explanation:

Through the process of photosynthesis, plants convert carbon dioxide and water into glucose. Oxygen is the by-product of this reaction. Energy is also released during photosynthesis. Hence, the emission of carbon dioxide from automobile exhaust won't have harmful effects on most plants.

Carbon dioxide from automobile exhaust is one of the major reasons for global warming and ozone depletion Hence, it has adverse effects on the environment. Also, an increased amount of carbon dioxide has adverse effects on breathing mechanisms in humans. A wide number of respiratory diseases like asthma occur due to carbon dioxide from automobile exhaust.