Final answer:
Arthur's respect for tradition is best supported by the line stating he meant to keep a custom he had assumed in his noble way.
Step-by-step explanation:
The textual evidence that best supports the conclusion that Arthur respects tradition is option C) "And there was a custom, besides, that he meant to keep, that he had assumed in his noble way..." This line explicitly mentions a custom, or tradition, that Arthur is committed to upholding, indicating his reverence for tradition. The other options describe other qualities or actions of Arthur that do not directly relate to his respect for tradition.