Final answer:
The Green Knight was able to remain fearless because he was a 'supernatural being', which is part of his character in the medieval story 'Sir Gawain and the Green Knight.'
Step-by-step explanation:
The reason it was easier for the Green Knight to remain fearless when he was struck by the axe is 'b) He was a supernatural being.' The Green Knight, as a character in the chivalric romance 'Sir Gawain and the Green Knight,' embodies various magical and otherworldly qualities, which allow him to face mortal challenges without fear.
His supernatural essence grants him abilities beyond those of normal human beings, thus enabling him to participate in seemingly lethal exchanges without concern for his own life.
The Green Knight was able to remain fearless when struck by the axe because he was a supernatural being and had enchanted armor. As a supernatural being, he possessed powers beyond those of a normal human, which allowed him to withstand the strike without fear. Additionally, his enchanted armor provided him with protection and made it easier for him to remain fearless.