This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Which of the following is the preformed toxin involved in mechanism of allergic rhinitis ? 
Select and explain. 
A. Histamine, B. Leukotriene, C. TXA2, D. PGD2
A: Histamine
Answer: A: Histamine 
Explanation: Ans. is 'a' i.e., Histamine