Finnish author Jaakko Mikkeli was accused by Norwegian author Kirsten Halden of plagiarizing a book that she had written and that had been published 20 years before Mikkeli’s. The two books, although set in different periods and regions, contain enough plot similarities to make coincidental resemblance unlikely.
Your task
Find the assumption the argument requires in order for its conclusion to hold.
Common trap
Answers that would help the argument but aren't strictly required (sufficient, not necessary).
Winning move
Negate each choice — the right one breaks the argument when negated.