The correct answer is B. Setting affects character behavior, which drives the plot.
Explanation:
Setting refers to the time and location (place) in which the events of a story take place in a narrative including historical period, cultural context, geographical conditions and the hour. The setting is considered as the story world and context in which all the actions in a story develop, considering this, the setting in a story whether is fictional or not is quite important as it usually affects the way characters behave and the actions they initiate according to the way they relate to the setting, also it can influence the characters' values as they are linked to the historical period and cultural contexts of them which is connected to the plot as the actions the characters develop determine the main event in a story (plot).
The one that would not contribute to the structure of Longfellow’s poem would be repetition of phrases. So, C.