Which of the following statements is false?
a. COPD has three subclasses: emphysema, small airway disease, and chronic bronchitis.
b. An obstructive disease pattern is characterized by increased airway resistance, which makes expiration difficult.
c. Asthma is characterized by bronchoconstriction, airway inflammation, and excessive mucus secretion.
d. Research has demonstrated that cigarette smoking only marginally increases the risk of lung cancer.