Answer:
b. Psychological contract
Explanation:
Psychological contract is the unwritten agreement between an employee and an employer. Based on the employees befforts and skills he will receive incentives from the employer. Incentives can be intangible like job security, or tangible like promotions and pay raises.
Bill Walters has an intangible contract with Amazon.com where he will receive promotions and pay raises based on his efforts and performance.