Katrina Is Trying to Put a Coin into a Vending

Multiple Choice

Katrina is trying to put a coin into a vending machine in her office. Sometimes the machine will take a coin on the first try, other times it can take up to five or six tries before the coin is finally accepted. On which type of schedule is inserting a coin into the vending machine reinforced, in this example?

A) intermittent
B) short-delay
C) continuous
D) noncontingent