Answer:
B. The morality of fair play.
Step-by-step explanation:
In the 14th Century chivalric tale of the Middle English era, "Sir Gawain and the Green Knight", the main themes of chivalry, honor and loyalty were predominant in all aspects of life. This was evident even between enemies who would not do anything against any unfair means, keeping one's honor and promise.
From the given passage, the Green Knight had come to the court of King Arthur to challenge his men in a game. If he had really wanted to do anything, he could easily kill or chose anyone and defeat him. But, he insist on a fair game, giving them the choice to send anyone fit or worthy enough to defend the king or worthy/ brave enough to fight him (the Green Knight). This refusal to fight "beardless boys" and instead looking for a man "strong enough to be worth riding against", he exhibits the chivalric nature of having a morally fair play against them.