Large amounts of traffic in many cities in the region a. cause air pollution
b. is an issue only in a few isolated areas
c. is not a problem since governments work to limit pollution

cause air pollution

Explanation:

air pollution is usually caused by cars and transportation such as trains,motorbikes and trucks

d. stage 4

explanation:

the existence of some kind of demographic transition is widely accepted in the social sciences because of the well-established historical correlation linking dropping fertility to social and economic development.[1] scholars debate whether industrialization and higher incomes lead to lower population, or whether lower populations lead to industrialization and higher incomes. scholars also debate to what extent various proposed and sometimes inter-related factors such as higher per capita income,lower mortality, old-age security, and rise of demand for human capital are involved.[2]