Roberta Has Been Studying Very Hard and Finds Out That

Roberta has been studying very hard and finds out that she has received an A+ on her English test.Her parents praise her and take her out to buy a new summer outfit.She is so happy that her parents are proud of her that she studies even harder for the next English test.This is an example of

A) positive reinforcement.
B) negative reinforcement.
C) partial reinforcement.
D) extinction.