Which sentence has an infinitive that functions as an adverb?
a. after the study of lizards, the naturalist planned to travel to remote lizard habitats. b. the librarian’s suggestion—to read the newest magazine article about large lizards—was a good one!
c. all of the students expressed their desire to see the series chronicling the life of a komodo dragon.
d. everyone in the group thought the komodo dragons were interesting to see.

A. After the study of lizards, the naturalist planned to travel to remote lizard habitats.

Explanation:

In this case, after the study of lizards, the speaker planned something. What he planned is modified by another verb. He planned "to travel to remote lizard habitats."

So, in this case, we have an infinitive phrase where "to travel" is modifying the verb "to plan."

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.