Competitive agonist and antagonist drugs ______________________.
|  | 
   |  | are direct agonists and antagonists; | 
   |  | are indirect agonists and antagonists; | 
   |  | have an affinity for a neurotransmitter's primary receptor site; | 
   |  | alternatives a and c are correct; | 
   |  | alternatives b and c are correct; | 
   
    
    
   
   
   [Review Part 1 of the tutorial]
   [Review Part 2 (Matching) of the tutorial]