Step 1: Understanding the role.
A housekeeping supervisor is responsible for managing and overseeing cleaning staff in hotels, hospitals, or organizations.
Step 2: Evaluating options.
(A): Correct. They supervise housekeepers.
(B): Customers are served, not supervised.
(C): Salesmen belong to sales department.
(D): Cashiers handle transactions.
Step 3: Conclusion.
Thus, a housekeeping supervisor supervises housekeepers. Final Answer:} Housekeepers.