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: Pharmacology
Vasodilatation is caused by: 
Select and explain. 
A. Serotonin, B. Histamine, C. LT C4, D. Thromboxane A2
B: Histamine
Answer: B: Histamine 
Explanation: Ans. B. Histamine* Histamine causes marked dilatation of smaller blood vessels that include aerioles, capillaries, and venules.