Final answer:
The option that is not an essential managerial function is demonstrating. Essential managerial functions include leading, controlling, planning, and organizing.
Step-by-step explanation:
Of the options provided, the one that is not an essential managerial function is C. demonstrating. The essential managerial functions include leading, controlling, planning, and organizing. These are commonly recognized as the four fundamental pillars in the field of management. Demonstrating is not typically categorized as a formal managerial function within this context.