Oído.
Since the infinitive verb is oír, which stems ends with a vowel (i in this case), we replace the inifinitive part ir with oído. Remember to include the accent since its an irregular form.
Está makes sense when u read it outloud
Viven, Yo=o unless irregular tú=as/es Ello, ella, usted= a/e, nosotros/nosotras=amos/imos/emos, ellos,ellas,ustedes=an,en
