Answer:
I believe the author's decision to use the word crusade to describe a protest movement affects the text in the sense that:
A. It makes the protest sound especially strong and committed.
Step-by-step explanation:
The Crusades were religious wars organized by the Catholic Church with the purpose of stopping the growth of Muslim states. Those battles lasted for centuries, and the soldiers fighting in them often perceived their own participation as a means of redemption and expiation for their sins.
Nowadays, when we refer to something as a crusade, we mean we are willing to commit to it. We know it will be a long and arduous path/journey to achieve whatever purpose we have, but we are willing to remain strong. The word is now free of its religious meaning, applying to any event or enterprise that demands effort, patience, and time. Having that in mind, we can choose letter A as the best option: It makes the protest sound especially strong and committed.
NOTE: The question does not make it clear how many options may be checked. If it is only one, then letter A seems to be the best. However, if you can check more, I would suggest adding letter C as well.