The description of Britain being "in jeopardy" while the ambitious barons

fought for the throne suggests the theme that

B. Strong leadership is important for a country's security.

Explanation:

The legendary story of Thomas Malory's The Crowning of Arthur tells how King Arthur became to be the heir for the throne of Britain. Arthur was the son of King Uther and Igraine, conceived the night her first husband the Duke was killed in battle.

After the death of King Uther, since the prince Arthur was still a young bo, the "ambitious barons fought one another for the throne, and the whole of Britain stood in jeopardy". This shows how a strong leader is needed for a nation to be secure and stable. So, with the absence of a suitable king, the whole country turned into chaos.