Sometimes, when one calls a customer service center, one is put on hold; one does not know how long it will be before the holding behavior is reinforced by the response of an associate, and it doesn't matter what one does in the meantime. holding a phone line is reinforced on a schedule.

variable-interval                                    

Explanation:

Four types of reinforcement schedules exists:

1. Fixed-ratio schedule.

2. Fixed-interval schedule.

3. Variable-ratio schedule.

4. Variable-interval schedule.

Variable-interval schedule: This is one of the reinforcement schedule which is used in operant conditioning. In a variable-interval schedule, the reinforcement is being given to a response after every particular time that has been passed, and the time provided is considered to be as unpredictable, yet the time is classified to be as on a variable or changing schedule.

Hence, in the given question, holding the phone line is reinforced on a variable-interval schedule.

which sentences ? that question is incomplete

answer; ha,ha,ha, corn on the cop;