Vi) May be they went away. (Rewrite using may might, most or canot,)
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might be they went away

Explanation:

hope this is the correct answer because

forget,it's nothing

is there an image you meant to add?

explanation:

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.