Answer:
<em>The sentence's complete linking verb is "</em><em>might have been."</em>
Explanation:
A <u>linking verb</u> reveals a relationship between the subject and the complement, that is the part of the sentence that follows the verb, because it provides information about that subject. Unlike other verbs, <u>linking verbs</u> carry no action: they simply link the subject to its complement.
Some of the most common examples of linking verbs are <em>to become, to appear, to seem</em>, or <em>to be</em>. This last verb is the one used in the sentence, and its full form in this case uses a modal verb -<em>might</em>- and the present perfect form.