Answer:
Have been
Step-by-step explanation:
Verbs that serve as connections of the subject and other extra information are described as linking verbs. The verb does not show the subject; instead, they link the subject together to form a complete and readable sentence. Commonly the words used in connecting the verb are (to be); however, many other linking verbs are used.
It is essential to remember that the verb connection does not show the action, but it only joined the subject with other additional information to complete the sentence.