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
[{'content': 'A patient is having a malignancy and has been suffering from severe pain. Which of the following opioid analgesics can be used as a transdermal patch for the alleviation of pain in him? \nSelect and explain. \nA. Morphine, B. Pentazocine, C. Fentanyl, D. Tramadol', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]