WILL PICK BRAINEST

As the population of a city recently grew , so did the number of cars and industries in the area. The local news started to post air quality warnings. What most likely caused the need for air quality warnings?

a-AS the population grew, more people wanted to know about air quality.
b-The removal of trees led to increased soil erosion
c-The level of carbon monoxide increased as people heated their homes.
d-More cars and industry led to increased carbon dioxide and nitrogen oxide emissions.