30. According to the passage, which of the following statements is true? (A) Patients should continue taking antihistamines for at least six weeks after the allergy season. (B) All three types of allergy medications discussed can be purchased without a prescription. (C) Oral antihistamines are more effective than nasal steroids for symptom relief. (D) Cromolyn cures allergies, while antihistamines and steroids only treat allergy symptoms.