The answer is is a verb that connects the subjects of a sentence to the complement
Linking verbs do not express action. Instead, they connect the subject of the verb to additional information about the subject. Look at the examples below:Keila is a shopaholic.Ising isn't something that Keila can do. Is connects the subject, Keila, to additional information about her, that she will soon have a huge credit card bill to pay.During the afternoon, my cats are content to nap on the couch.Areing isn't something that cats can do. Are is connecting the subject, cats, to something said about them, that they enjoy sleeping on the furniture.After drinking the old milk, Vladimir turned green.Turned connects the subject, Vladimir, to something said about him, that he needed an antacid.