Which one of the following sentences contains a predicate adjective?
a. i brought my lunch for the first time this year.
b. the teacher appeared angry when dave forgot his homework.
c. what does this hard lesson teach you?
d. we scanned the distant shore for signs of life.

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.