Question

smoking:
increases levels of hemoglobin
decreases levels of hemoglobin

Explanation:

Smoking causes carbon monoxide (CO) to bind to hemoglobin, which reduces the ability of hemoglobin to carry oxygen. However, the body may respond by increasing the production of red blood cells (and thus hemoglobin) to try to compensate for the reduced oxygen - carrying capacity, but the functional capacity of hemoglobin is decreased. But in terms of the level of hemoglobin (the amount of hemoglobin protein), smoking can lead to an increase in hemoglobin levels as the body tries to make up for the impaired oxygen transport due to CO binding. So the correct option is the one that says "Increases levels of hemoglobin".

Answer:

A. Increases levels of hemoglobin