John's Parents Promise Him a Prize If He Finishes Reading

Multiple Choice

John's parents promise him a prize if he finishes reading 20 books.John reads the first 19 books without reinforcement because he knows that the payoff will occur when the last book is completed.Which type of partial reinforcement schedule is being discussed here?

A) Fixed-interval schedule
B) Variable-interval schedule
C) Fixed-ratio schedule
D) Variable-ratio schedule