Which of the following was a key feature in Stephen Covey's book, The Seven Habits of Highly Effective People: Powerful Lessons in Personal Change?

A. He discussed how a leader's success hinges on balancing personal and professional effectiveness.

B. He focused on the strategic and organizational challenges confronting managers in multinational corporations.

C. He discussed "management by objective" (MBO), by which a manager should be self-driven to accomplish key goals that link to organizational success.

D. He analyzed 1,435 companies to understand why some companies reach high levels of sustained performance while other companies fail to reach greatness.