The verb "competir" is a stem-changing verb in the present tense. For the forms excluding "vosotros" and "nosotros," it undergoes a vowel change from "e" to "i." Here are the present tense forms:
- Yo compito
- Tú compites
- Él/Ella/Usted compite
- Ellos/Ellas/Ustedes compiten
So, the stem change occurs in "tú," "él/ella/usted," and "ellos/ellas/ustedes" forms, changing from "e" to "i."