Here's why:
* Direct objects receive the action of a verb. They answer the question "What?" or "Whom?" after the verb.
* Example: "She ate the apple." (Apple is the direct object)
* Subject complements describe or rename the subject of a sentence. They usually follow linking verbs (like "be," "seem," "become," etc.).
* Example: "He is a doctor." (Doctor is the subject complement)
Not all verbs can take both direct objects and subject complements.
* Transitive verbs require a direct object.
* Example: "He threw the ball." (Throw requires a direct object)
* Intransitive verbs do not take a direct object.
* Example: "The bird sings." (Sings doesn't need a direct object)
* Linking verbs take subject complements.
* Example: "The sky is blue." (Blue is the subject complement)
Therefore, a verb's ability to take a direct object or a subject complement depends on its grammatical function and type.