This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Which of the following is true for receptor action of the drug 
Select and explain. 
A. An antagonist has both an intrinsic activity and affinity for receptor, B. An antagonist has the affinity but no intrinsic activity for the receptor, C. A paial antagonist has no affinity or intrinsic activity for the receptor, D. Intrinsic action and affinity are not impotant for drug action
B: An antagonist has the affinity but no intrinsic activity for the receptor
Answer: B: An antagonist has the affinity but no intrinsic activity for the receptor 
Explanation: Ref-KDT 6/e p41 Intrinsic activity is a measure of the ability of a drug that is bound to the receptor to generate an activating stimulus and produce a change in cellular activity. Both agonists and antagonists can bind to a receptor.