Which of the following statements is(are) true for neurotransmitter agonists?
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   mimics the natural effects of a neurotransmitter; | 
   
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   has the ability to bind to a neurotransmitter receptor site; | 
   
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   opposes the natural effects of a neurotransmitter; | 
   
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   does not have the ability to bind to a neurotransmitter site; | 
   
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   both a and b above are correct; | 
   
   
   
   
   
   [Review Part 1 of the tutorial]
   [Review Part 2 (Matching) of the tutorial]