In her Book of Common Sense Etiquette (1962), former first lady Eleanor Roosevelt wrote, "True patriotism springs from a belief in the dignity of the individual, freedom and equality not only for Americans but for all people on earth, universal brotherhood and good will, and a constant striving toward the principles and ideals on which this country was founded."

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.

a. is the correct answer