1. Correr
Tú
2. Correr
Yo
3. Correr
Sara y Ana
4. Correr
Usted
5. Correr
Ustedes
6. Correr
La gente
7. Correr
Marcos y yo 8. Carolina la maleta.9. Yo las ventanas.10. Nosotras los libros.11. Usted el cuaderno.12. Tú la ventana.13. Ustedes las maletas.14. Los muchachos los cuadernos.

1. Tú corres.

2. Yo corro.

3. Sara y Ana corren.

4. Usted corre.

5. Ustedes corren.

6. La gente corre.

7. Marcos y yo corremos.

8. Carolina corre la maleta.

9. Yo corro las ventanas.

10. Nosotras corremos los libros.

11. Usted corre el cuaderno.

12. Tú corres la ventana.

13. Ustedes corren las maletas.

14. Los muchachos corren los cuadernos.

Explanation:

we must identify the grammatical person at each point and conjugate the verb run for each of them in the present. It is important to identify the person, time and gender to be able to correctly conjugate the verb and that it has agreement with what is being expressed.

corras is the only one that is informal but doesn't follow the suffix rule. correr is the verb. corre is the formal verb form. corra would be used as the formal is corre ended with an a.

your best bet would be corras, it's the only one that is informal but is still wrong