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
Which of the following is true for receptor action of a drug: 
Select and explain. 
A. An antagonist has both intrinsic activity and affinity for receptor, B. An antagonist has affinity but no intrinsic activity for receptor, C. A partial antagonist has no intrinsic activity or affinity for receptor, D. Intrinsic activity and affinity are not important for drug action
B: An antagonist has affinity but no intrinsic activity for receptor
Answer: B: An antagonist has affinity but no intrinsic activity for receptor 
Explanation: None