An employer retained a third-party administrator ("TPA") to manage the day-to-day operations of its ERISA-covered 401(k) retirement plan that it sponsored for its employees. The TPA, in turn, hired a third-party investment manager to invest the plan's assets. Under this arrangement, the employer has an ERISA duty to: An employer retained a third-party administrator ("TPA") to manage the day-to-day operations of its ERISA-covered 401(k) retirement plan that it sponsored for its employees. The TPA, in turn, hired a third-party investment manager to invest the plan's assets. Under this arrangement, the employer has an ERISA duty to: A. A. Do nothing because it retained a third party administrator to manage the day to day operations of the Plan. B. Monitor the investment of the plan assets to protect against imprudent investments. C. Monitor the investment of the plan assets to ensure no losses result from the investment. D. All of the above.