Answer:
1. Ella piensa.
2. Yo entiendo.
3. Marlena y yo dormimos.
4. Tú mueres.
5. Carlota y Sara se encuentran.
6. Ustedes prefieren.
7. Vosotros perdéis.
8. Yo juego.
Explanation:
When verbs have these root changes, it is because they are expressed in the present tense. Therefore it is important to identify the person, the number and the gender in each sentence to conjugate the verb logically and to be consistent with what is being expressed.