Task: Question Answering
Input (English): Question: It has been proven that amphetamines have reinforcing effects because: 
 Options:  <1> They are GABAergic agonists. <2> They are dopaminergic antagonists. <3> They are serotonergic antagonists. <4> They are dopaminergic agonists. <5> They are serotonergic agonists.
Output (English): 4