The correct answer to this question is Its more challenging to diffuse things in and out of the lungs. Alveoli's are air sacs within the lungs. They are tiny and resemble clusters of grapes. The number of alveoli is the person has based on the size of their lung, but it can range from 274 million to 790 million.
Alveolus help passes oxygen through so that they can enter the bloodstream. Over time, smoking causes damage to the alveolus. The smoke from the cigarette breaks the walls of the alveoli, making the air sacs to be less effective when passing the oxygen.