Final answer:
The factor that contributes to South Asia's environmental challenges mentioned in the options is pollution from motor vehicle exhaust.
Step-by-step explanation:
South Asia's environmental challenges are influenced by several factors, including population growth, pollution from motor vehicle exhaust, deforestation, and industrial activities. One of the factors contributing to environmental issues in South Asia is pollution from motor vehicle exhaust. The rise in the number of vehicles, combined with insufficient emission controls, leads to significant air quality deterioration. Deforestation also plays a crucial role, as the growing demand for wood used in cooking and construction has resulted in widespread tree cutting. Moreover, industrial growth has led to other types of pollution that further degrade the environment.