You Walk Up to a Soda Machine and Put in a Dollar

Multiple Choice

You walk up to a soda machine and put in a dollar, and are rewarded with a bottle of root beer. When you put in another dollar, you get another soda. Assuming that the machine has a limitless supply of root beer, which kind of reinforcement schedule does this machine operate on?

A) partial reinforcement
B) interval reinforcement
C) continuous reinforcement
D) ratio reinforcement