Fixed interval Fixed interval drop zone empty. Variable interval Variable interval drop zone empty. Fixed ratio Fixed ratio drop zone empty. Variable ratio Variable ratio drop zone empty. Appreciating the positive performance of an employee only once every two weeks and not at any other time Rewarding a salesperson for an e-learning company for each dollar of revenue above $10,000 for which they receive a 10 percent commission Promoting an employee to a higher-level position Randomly checking the quality of an employee's work and praising the employee for good work