The 5-year-old child of two very busy parents has been throwing tantrums. Whenever the child gets angry or upset the parents immediately fuss over the child. Nevertheless, the child's tantrums do not diminish. In fact, they seem to occur more often. We may assume that the parents' fussing over this child serves as a(n) ________.

A) unconditioned response
B) positive reinforcer
C) punisher
D) negative reinforcer

The parents' fussing over the child when they throw tantrums serves as a positive reinforcer, meaning it increases the likelihood of the child's tantrums occurring again in the future. The child has learned that throwing a tantrum will result in attention from their busy parents, reinforcing the behavior. Therefore, the parents should try to ignore the tantrums and only provide attention when the child is calm and behaving appropriately.