This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti-Neoplastic Agents, Subject name: Pharmacology
Which of the following opioid is used by transdermal route in cases of malignancy associated pain - 
Select and explain. 
A. Fentanyl, B. Morphine, C. Codeine, D. Oxycodone
A: Fentanyl
Answer: A: Fentanyl 
Explanation: Ans. is 'a' i.e., Fentanyl o Fentanyl is opioid analgesic used via transdermal delivery systems in case of chronic pain.