Transform the sentence "He did not finish his homework" using "should have".

The transformation using "should have" effectively conveys the idea that there was an expectation for him to finish his homework, which he ultimately did not fulfill. The structure "should have finished" indicates a past obligation or expectation that was not met, aligning perfectly with the original sentence's meaning. This transformation captures both the intention of the original statement and introduces a sense of regret or criticism regarding the incomplete homework.

In contrast, other options either do not convey this sense of obligation or incorrectly apply the auxiliary verb “should.” For instance, one option suggests he should finish it in the present tense, losing the context of a past action that was not completed. Another option implies that he should not have finished, which alters the meaning entirely, suggesting that finishing homework was unnecessary. Lastly, stating that he must have finished implies certainty about the completion of the homework, rather than an acknowledgment of the failure to complete it. Therefore, the correct choice accurately reflects the original sentence with the correct use of "should have."