What's the most efficient way to get the opinions of experts on any writing topic? A. Contact them via email.
B. Call them and set up interviews.
C. Contact their publishers.
D. Do research at a library.

this is b. how railways dealt with people riding the trains without paying

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.

the answer is c because info security should not use them for code

the answer is c the speaker emotions