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: Anaesthesia
At the end of a balanced anaesthesia technique with non-depolarizing muscle relaxant, a patient recovered spontaneously from the effect of muscle relaxant without any reversal. Which is the most probable relaxant the patient had received. 
Select and explain. 
A. Pancuronium, B. Gallamine, C. Atracurium, D. Vecuronium
C: Atracurium
Answer: C: Atracurium 
Explanation: C i.e. Atracurium