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 does not run out 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