What is the cause to air pollution??? please help me

Select the correct answer.look at this nineteenth-century illustration of london. which explanation best relates this illustration to changes in britain in the 1800s? a.factory workers in cities lost their livelihood because of the lack of housingb.industrialization narrowed the inccome gap between landowners and workers.c.the migration of workers from rural to urban areas resulted in overcrowded citiesd.the spread of railways allowed farmers to sell produce far from where it was grown.