The knights of the round table express their solidarity by wearing a green girdle as gawain does. why does gawain wear the green girdle?
a. as a symbol of his courage
b. as a mark of honor
c. to show his love for nature
d. as a symbol of his weakness

Gawain wear the green girdle as a symbol of weakness .

D

Explanation

Gawain had previously wore the green girdle as a symbol of survival as directed by his lover.

However, after he fails, Gawain wore the green girdle with the purpose to own his weaknesses and misdemeanour.

The green girdle was a reminder to him and everybody else that one can only forget his/her iniquities but cannot erase them.  

The Knights however wore the green girdle to commemorate Gawain as a symbol of honor.

From the knight's perspective the girdle won in remembrance of Gawain doesn't symbolize failure as it did before.