During the child's first visit, the dentist requested that the parents wait in the reception room. The child cried moderately, but tearfully, throughout the dental examination and prophylaxis. The dentist "gave her permission" to cry while he/she worked and then took no notice of her crying. Her crying diminished in intensity over time and then stopped. With respect ONLY to the crying behavior, the dentist has)A. used positive reinforcement.B. used negative reinforcement.C. extinguished the behavior.D. ignored the problem.