Which feature shows that management principles are not limited only to books?

Correct answer: Practical usefulness

The governing concept is the practical nature of management principles. These principles are developed from managerial observation, experience and analysis, and they are intended to help managers deal with actual organisational problems. A manager may use them while assigning duties, resolving conflict, coordinating departments, motivating employees or balancing organisational objectives. Their value is therefore demonstrated through application, not through memorising definitions alone. Option A is correct because practical usefulness shows that principles operate in real workplaces. Secrecy has no connection with their nature, irrelevance contradicts their purpose, and permanent rigidity is incorrect because principles must be adapted to circumstances.