Problems with aggressive wildlife often begins with aggressive human beings.

answer: d.she abandons people when they least expect it.

in the monk's tale, we encounter seventeen stories that relate historical events. all of these stories have tragic commonalities. they tell the stories of heroes who, despite their success in life, all met sad ends. the monk blames these sad outcomes on fortune. one of fortune's traits is that she abandons people when they least expect it. this is one of the most common themes of medieval tragedies.

quite an interesting way to teach topic sentences, because the answer to this question is the best definition of a topic sentence that one can present, it is as if answering the questions taught you how to do it, this is some real teaching, it is terribly well-done.

the topic sentence in this paragraph is:

topic sentences writers stay on track and keep a paragraph from becoming an aimless collection of sentences about an idea.

which incidentally tells you what a topic sentence should be.