Final answer:
The revised sentence for pronoun-antecedent agreement is 'The class completed its assignment,' where 'its' correctly matches the singular antecedent 'the class.'
Step-by-step explanation:
The sentence 'the class completed their assignment' requires revision for proper pronoun-antecedent agreement. In English grammar, an antecedent is a noun or noun phrase to which a pronoun refers. It is important for a pronoun to agree in number and gender with its antecedent. In this case, 'the class' is a collective noun that is treated as singular; hence, the correct possessive pronoun should also be singular. The revised sentence should read: 'The class completed its assignment.'