Jonas has homework, but it isn't finished. Jonas has homework that isn't finished.
Answer:
Jonas has homework, but it isn’t finished.
Jonas has homework that isn’t finished.
Jonas has homework; isn’t finished.
Explanation:
Compound sentences have at least two independent clauses, which can be joined by a comma and a coordinating conjunction, or by semicolon. Besides, in this case, the clauses can be also linked by the relative pronoun that, since the phrase isn't finished works as an adjective that modifies the noun homework, creating as a restrictive clause.
