I'd say that the plot element that is most prominent in "The Knight's Tale" from Canterbury Tales is C. battling suitors.
The story is about two young man who fight for the love of a beautiful woman. In the end, one of them dies, and the other one gets to marry her.
While the main idea is usually in the first sentence, the next most common placement is in the last sentence of a paragraph. The author gives supporting information first and then makes the point in the last sentence. Here's a paragraph we can use as an example. Try to locate the topic and the main idea.
I BLIVE THE RIGHT ANSWER IS C