Final answer:
Subjective complements describe or redefine the subject, often following linking verbs. They are not to be confused with objects, which receive the action of transitive verbs. Hence, subjective complements are not objects. Option A is correct.
Step-by-step explanation:
Subjective complements are complements of verbs that describe or redefine the subject, typically following linking verbs such as seem, look, smell, sound, and become. These can take the form of noun phrases (NP) or adjectives. However, subjective complements are not objects of the verb; they do not receive the action as direct objects do in a sentence structure involving transitive verbs. Instead, subjective complements relate back to the subject to provide additional information or identification.
Given this understanding, the correct answer to the student's question, 'Subjective complements are NP complements of verbs but aren't _________.' is a) Objects.