Which of the following lines best presents the dominant moral of "the monk's tale"?

a. he was a soldier with a manly heart / so dear to him was honest decency
b. thus fortune with a light / turn of her wheel brings men from joy to sorrow.
c. he swore to sin no more, until the hour / of death when at last he was interred, / he recognized god's mercy and his power.
d. and then he saw that of his own perdition / he was sole author and he fled away.