The heading that best completes the partial outline would be:
II. Ancient Civilizations and Philosophies.
The heading that best completes the partial outline is "B) Zhou Dynasty." The outline seems to be organizing historical developments, and the Zhou Dynasty is closely associated with both the "Period of Warring States" and the "Development of Daoism" in ancient China.
The Zhou Dynasty (1046–256 BCE) followed the Shang Dynasty and preceded the Qin Dynasty. During the Zhou Dynasty, China experienced significant political, social, and philosophical developments, including the emergence of Daoism as a major philosophical and religious tradition.
The "Period of Warring States" refers to the later years of the Zhou Dynasty characterized by internal conflict among regional states.