Which of the following verbs is not a stem-changing verb? perder entender correr comenzar

Let’s begin by the fact that a verb in infinitive has two parts:

-The ending: ar, er, ir

-The stem, which is is everything else (except the ending, of course)

For example, the Spanish verb jugar (to play)

The ending is ar

The stem is jug

Now, some Spanish verbs change their stem in a predictable way when they are conjugated. These are called stem-changers  or stem-changing verbs.

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

According to the explanation above, the only verb of the list that is not a stem-changer is correr (to run), because this verb does not follow the rules.

Let's prove it  by conjugating this verb in present with the difeerent personal pronouns. Note the stem corr keeps the same:

1st person singular Yo: corro

2nd person singular (informal) Tú: corres

2nd person singular (formal) Usted: corre

3rd person singular El/Ella/eso/esa: corre

1st person plural Nosotros: corremos

2nd person plural Ustedes (In latinAmerica): corren

2nd person plural Vosotros (In Spain): corréis    

3rd person plural Ellos/Ellas: corren