Answer:
"often considered witty"
Explanation:
A subject complement is a word that describes the subject of a sentence that follows immediately after a linking verb. Like the name suggests, it complements the subject. It can either be a noun, adjective or pronoun.
Therefore, the subject complement from the sentence "Bret Hartes' poems and prose were often considered witty" is "often considered witty".
The correct answer to this question is the second one “to state the writers opinion”