This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pharmacology
Drug directly acting on blood vessels is: 
Select and explain. 
A. Hydralazine, B. Verapamil, C. Propranolol, D. Methyaldopa
A: Hydralazine
Answer: A: Hydralazine 
Explanation: Ref:KDT 6/e p547 Some drugs used to treat hypeension, such as calcium channel blockers -- which prevent calcium from entering blood vesselwalls -- also dilate blood vessels. But the vasodilators that work directly on the vessel walls are hydralazine and minoxidil.