John, a sales manager, told his new hire, Stephanie that he hired her because she has potential to be a great salesperson. Stephanie was a very shy person by nature, but after this motivational talk, she tried hard to practice her communication skills and went out of her way to get clients. Stephanie was awarded the "Salesperson of the Year." What happened to Stephanie can be best explained by which of the following concepts? 

a. self-serving bias.

  b. fundamental attribution error. 

 c. social comparison.  

 d. self-fulfilling prophecy.