The correct answer is option 'A': Flat structure of organization.

Explanation:
Neoclassical organization theory is a management approach that focuses on the human aspect of organizations. It emerged as a reaction to the classical management theories that emphasized the rational and efficient use of resources. Neoclassical theorists believed that organizations are social systems and that the behavior of individuals within the organization is influenced by their social and psychological needs.

The key emphasis of neoclassical organization theory is on creating a flat structure of organization. This means that the organization has a minimal number of hierarchical levels and a wide span of control. In a flat structure, there are fewer layers of management, which allows for quicker decision-making, better communication, and increased employee autonomy and empowerment.

The flat structure of organization is in contrast to the tall structure, which is characterized by a large number of hierarchical levels and a narrow span of control. In a tall structure, there are many layers of management, resulting in slower decision-making, more bureaucracy, and limited employee empowerment.

Neoclassical organization theory also recognizes the importance of coordination within the organization. However, instead of relying solely on hierarchical coordination (coordination by hierarchy), neoclassical theorists emphasize the importance of informal coordination mechanisms such as peer-to-peer communication, teamwork, and collaboration. These informal coordination mechanisms are believed to be more effective in dealing with the complexity and uncertainty of organizational tasks.

Unity of command, on the other hand, is a principle of classical organization theory that states that each employee should have only one direct supervisor. Neoclassical organization theory challenges this principle by recognizing the importance of lateral communication and collaboration among employees, which may involve multiple supervisors or managers.

In summary, neoclassical organization theory emphasizes the flat structure of organization as it enables quicker decision-making, better communication, and increased employee autonomy. It also recognizes the importance of informal coordination mechanisms over hierarchical coordination and challenges the classical principle of unity of command.