Final answer:
Self-stimulatory behavior is repetitive non-purposeful movements or sounds such as hand-flapping, rocking back and forth, or making repetitive vocalizations.
Step-by-step explanation:
A. True
Self-stimulatory behavior is indeed repetitive non-purposeful movements or sounds. These behaviors, also known as stimming, are commonly seen in individuals with autism spectrum disorder (ASD) or other developmental disabilities. Stimming can include actions such as hand-flapping, rocking back and forth, or making repetitive vocalizations.