Which sentence demonstrates correct subject-verb agreement?

The sentence "The puppies are house trained" demonstrates correct subject-verb agreement because the plural noun "puppies" agrees with the plural verb "are." In English grammar, subject-verb agreement requires that the subject and verb match in number; in this case, since "puppies" refers to more than one puppy, the correct form of the verb is "are," which is used for plural subjects.

Additionally, the other choices exhibit errors in subject-verb agreement or verb forms. The first choice incorrectly uses "is" with the plural subject "puppies." The second choice incorrectly pairs "are" with the singular subject "puppy." The final choice mistakenly uses the incorrect verb form "house train" rather than the correct past participle "trained" for the singular subject "puppy." Thus, the correct answer supports the fundamental grammatical rule of maintaining agreement in number between subjects and verbs.