explain how stem-changing –ir verbs are different from stem-changing –ar and –er verbs in the present subjunctive.

short answer

Stem-changing -ir verbs in the present subjunctive follow the same pattern as -ar and -er verbs when it comes to changing the stem vowel in certain forms. However, the stem changes occur in different conjugations for -ir verbs compared to -ar and -er verbs. Additionally, the endings for -ir verbs in the present subjunctive are different from those of -ar and -er verbs.