Which Promotion Exemplifies the Use of a Variable-Ratio Schedule of Reinforcement

Multiple Choice

Which promotion exemplifies the use of a variable-ratio schedule of reinforcement?

A) Every now and then, a café announces a two-for-one deal.
B) A café offers its customers a punch card. Each time a patron purchases a beverage, a hold is punched; when ten holes are punched, the patron receives a free beverage.
C) A café prints "You are a winner" on a random one-twelfth of its coffee lids; patrons receiving such a lid can redeem it for a free beverage.
D) A café offers each patron an early morning two-for-one free-beverage-with-purchase deal from 5 to 6 a.m. on Monday mornings.