6. Why do cigarette smokers cough more than most people do?
(A) The tar in cigarette smoke tends to make alveoli stick closed. Coughing opens them.
(B) Coughing is the respiratory system's attempt to clear itself of the toxins found in smoke.
(C) Cigarette smoking partially paralyzes the lungs; coughing exchanges the resultant "dead air".
(D) Coughing stimulates blood flow to the lungs.
(E) By raising the pressure in the lungs, coughing forces more oxygen into the blood.