Which of the Following Is NOT True of Antihistamines

Which of the following is NOT true of antihistamines?

A) They compete with histamine in the respiratory tract to block their receptor sites.
B) They may be used for several years because tolerance does not develop.
C) They are chosen by their potency, duration of action, and incidence of side effects.
D) Their side effects include drowsiness and dry mouth.
E) They are used interchangeably to find the most effective agent for the patient.