Psychology review:
11. An executive in a stockbrokerage firm works with his office door closed. At the same time every hour he opens the door to see what his employees are doing. The employees have learned to work only during the five minutes before he opens the door. Their work pattern is typical of responses that are reinforced on a __________ schedule.
A. fixed-ratio
B. fixed-interval
C. variable-ratio
D. variable-interval