What is a person who witnesses a harmful act and takes some action against it?

boccaccio employs the voice of his narrator dioneo to represent his ideas on the tension between masculinity and femininity.  while dioneo excites the members of the brigata and recognizes women for their unique skills and independent ideas, he concludes the decameron with a story reminiscent of the society from which these young aristocrats escaped, revealing misogynistic overtones.  dioneo boccaccio is able to explore the gender disparity which is inherent in 14th century florentine society.

queen elizabeth's purpose in the passage is;

d. to persuade the troops that she is a capable commander

"i have the heart and stomach of a king. i myself will be your general, judge, and rewarder."

i think it is b. hope this !