The sentence that uses a semicolon correctly is the last choice: The author has written four other books; this is book five. The purpose of a semicolon is to first of all separate two different sentences. Its secondary purpose is to come in the place of a conjunction preceded by a comma and it can also take the place of a period. Hope that this answer helps you!
The correct answer for the first question would be: The author has written four other books; this is book five. (the other sentences could be corrected by simply using commas) And the correct answer for the second question is: probably: Most people eat cereal, it (im sure there was more to the sentence, but even if there wasn't, it didn't end with a period, therefore making it a run-on)
