Step 1: Understand the evolution of management thought.
Management theories developed in historical phases: the Classical approach (focused on structure, efficiency, and formal hierarchy), the Neo-Classical or Human Relations approach (focused on the human element), and later the Modern approach (focused on systems and contingency).
Step 2: Evaluate option (A) - Henri Fayol's principles.
Henri Fayol was the founder of the Administrative Management school, which is a branch of the Classical approach. He focused on top-down administrative principles for managing entire organizations.
Step 3: Evaluate option (B) - Taylor's Scientific Management.
F.W. Taylor belongs to the Classical Scientific approach. He focused on maximizing shop-floor efficiency through time-and-motion studies, standardization, and differential pay. Both Taylor and Fayol are Classical thinkers.
Step 4: Evaluate option (D) - Max Weber's bureaucracy.
Max Weber's Bureaucratic Model belongs to the Classical Structural approach. It emphasized formal rules, hierarchy, and impersonal authority. This too is a Classical theory.
Step 5: Evaluate option (C) - Elton Mayo's Hawthorne Studies.
Elton Mayo conducted a series of experiments at the Hawthorne Plant of Western Electric Company in Chicago. His findings revealed that worker productivity was strongly influenced by social factors, group dynamics, and managerial attention, not just physical work conditions. This humanistic focus founded the Neo-Classical (Human Relations) movement.
Step 6: Conclude the correct answer.
Among all options, only Elton Mayo and his Hawthorne Studies belong to the Neo-Classical approach.
\[ \boxed{ \text{Elton Mayo's Hawthorne Studies} } \]