Can someone explain to me why each one would be a performance obligation and why letter B is not. Thank you.

In which of the following is the option described not a performance obligation?

a) Customers accumulate points for every dollar spent at Madeline's Book store. The points can be redeemed for books once certain levels are met.

b) Customers can get 5% cash back for every $100 spent on eco-friendly products.

c) Customers can "buy two, and get one free" at a menswear store

d) Upon purchase of any name-brand TV, customers can purchase a 5-year extended warrant at a 25% discount