13. Tú repites
14. Ella compra
15. Nosotros ocurrimos
16. Yo ando
17. Ustedes beben
18. El deber
19. Usted llama
20. Ellas viven
21. Ellos creen
Answer:
the first one is estudian
It would tienes because it goes with tú. I'm not sure how to really explain it but that's the ser you would use with tú. I hope this helps!
