I believe the answer is: D. Because they tried to show that betrayal of knightly duties could be disastrous.
The term that used to refers to this type of betrayal is 'knightly treason'. King Arthur take the knight code very seriously, to the point where he established the Treason Act of 1351, which specifically highlight various type of actions or behaviours that can be considered as 'knightly treason' and deserve a legal punishment.
