Exposure to tobacco smoke immobilizes and destroys cilia. how might this effect explain why smokers have an increased incidence of coughing and respiratory infections?

Cilia is the structure that the body uses to trap particulates like dust and and dander, as well as pathogens like bacteria which cause major infections. These Cilia push such things back up the tract. If the Cilia is deteriated, the bacteria can easily move to the Bronchioles and cause infections.

The answer is either 3 or 4