Which does the author use to support the belief that adopted highways have less trash than non-adopted
highways?
a
testimony from lawmakers about trash found on adopted highways
b.
facts about highway patrolmen who have seen people who litter on highways
c
examples of people who have adopted highways and how it has changed their lives
cd
d.
statistics showing the difference in pounds of trash between the two types of highways

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.

he will find out what went wrong or happened and how.