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
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? 
Select and explain. 
A. Morphine, B. Pentazocine, C. Fentanyl, D. Tramadol
C: Fentanyl
Answer: C: Fentanyl 
Explanation: None