The correct answer is: D. unity of command.

Unity of command is a management principle that states that each employee should receive orders from and report to only one supervisor. This principle is important because it helps to ensure that employees are clear about who their boss is and that they are not receiving conflicting orders from different supervisors. It also helps to prevent confusion and chaos in the workplace.

Line of authority is the chain of command that exists in an organization. It is the line of communication that runs from the top of the organization to the bottom. The line of authority is important because it ensures that everyone in the organization knows who they are responsible to and who is responsible to them.

Centralization is the degree to which decision-making is concentrated at the top of an organization. A centralized organization is one in which most decisions are made by top management. A decentralized organization is one in which decisions are made at lower levels in the organization.

Unity of direction is a management principle that states that there should be one plan of action for a company or department. This principle is important because it helps to ensure that everyone in the company is working towards the same goal.