Answer: e → I stem-changing verb
Explanation: In Spanish grammar, a verb in infinitive has two parts:
-The ending: ar, er, ir
-The stem, which is everything else (except the ending, of course)
For example, the Spanish verb servir (to serve):
The ending is ir
The stem is serv
Now, some Spanish verbs change their stem in a predictable way when they are conjugated. These are called stem-changers or stem-changing verbs. In this sense, there are three basic different ways in which the stem of a verb can change in the present tense:
From e to ie
From o to ue
From e to i
Now for the verb servir (to serve), we are talking about the third case (From e to i). Let's prove it:
1st person singular Yo: sirvo
2nd person singular (informal) Tú: sirves
2nd person singular (formal) Usted: sirve
3rd person singular El/Ella/eso/esa: sirve
1st person plural Nosotros: servimos
2nd person plural Ustedes (In latinAmerica): sirven
2nd person plural Vosotros (In Spain): servís
3rd person plural Ellos/Ellas: sirven
Note that in a stem‐changing verb all forms of the verb will undergo a stem change except for Nosotros/Nosotras (we) and vosotros/vosotras (you).