This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anaesthesia, Subject name: Pharmacology
Patient undergoing surgery was given a muscle relaxant. It produced marked fall in B.P. and increase in airway resistance which were reversed with diphenhydramine. The muscle relaxant was most probably: 
Select and explain. 
A. Pancuronium, B. Diazepam, C. Tubocurarine, D. Vecuronium
C: Tubocurarine
Answer: C: Tubocurarine 
Explanation: Hypotension and bronchoconstriction (increase in airway resistance) are impoant adverse effects caused by histamine. This is confirmed to be due to histamine because of reversal with diphenhydramine. * Maximum histamine release is caused by d-tubocurarine. * Vecuronium does not cause histamine release, therefore is preferred agent in asthmatic patients.