Task: Explanation
Input (English): Question: Suppose that Mary smokes cigarettes for 20 years. If you measured the oxygen levels in her blood before she started smoking and compared them to oxygen levels later in her life, what would you find? 
 Answer: less oxygen in her blood later in life
Output (English): Smoking reduces the amount of oxygen available for diffusion at the lungs, so less oxygen gets absorbed and blood is oxygenated to a lesser degree.