Final answer:
In the scenario where a child is sent to a time-out for pulling his sister's hair, the discipline method demonstrated is positive punishment, which involves adding an undesirable stimulus to decrease a behavior.
Step-by-step explanation:
When a child reaches over and pulls his sister's hair and, as a result, his parents send him to the corner for a "time out," this example demonstrates c) Positive punishment. Positive punishment involves adding an undesirable stimulus to decrease a behavior. In this case, the undesirable stimulus of the time out is added to decrease the likelihood of the child pulling hair again.