A patient visits your clinic often with recurrent respiratory infections. Based upon their medical history, it appears they have been an active smoker for over 40 years. Select the statement that most accurately reflects how this information may reveal why the patient is highly susceptible to respiratory pathogens.

A. Smoking decreases the formation and effectiveness of complement proteins.

B. Smoking directly inhibits B- and T-cell action.

C. Smoking decreases the activity of neutrophils.

D. Smoking can paralyze the ciliary escalator.