In the Last 3 Months, Mike Never Knows When He

Multiple Choice

In the last 3 months, Mike never knows when he is going to get his allowance from his parents. He knows that he gets paid about every week, but sometimes his allowance comes 10 days after the previous one, sometimes only 4 days separate his allowance, while some payments come on a regular, 7-day rotation. The type of reinforcement schedule being used is a:

A) fixed interval
B) variable ratio
C) fixed ratio
D) variable interval