How did air pollution affect moth populations?

Industrialisation and domestic coal fires had caused sooty air pollution which had killed off lichens and blackened urban tree trunks and walls. So now it was the pale form of the moth that was more obvious to predators, while the melanic form was better camouflaged and more likely to survive and produce offspring.

For more information, check out these:

Moths count .org

Faunalytics .org

Wikipedia .org

answer; i believe the correct answer to the above question is ( friction)