Riothamus, a fifth-century king of the Bri

问题：

Riothamus, a fifth-century king of the Britons, was betrayed by an associate, fought bravely against the Goths but was defeated, and disappeared mysteriously. Riothamus’ activities, and only those of Riothamus, match almost exactly those attributed to King Arthur. Therefore, Riothamus must be the historical model for the legendary King Arthur.
The argument above requires at least one additional premise. Which of the following could be such a required premise

A．Modern historians have documented the activities of Riothamus better than those of any other fifth-century king.

B．The stories told about King Arthur are not strictly fictitious but are based on a historical person and historical events.

C．Riothamus’ associates were the authors of the original legends about King Arthur.

D．Legends about the fifth century usually embellish and romanticize the actual conditions of the lives of fifth-century nobility.

E．(E) Posterity usually remembers legends better than it remembers the actual historical events on which they are based.