Final answer:
The verb 'preferir' is a stem-changing verb that changes from 'e' to 'ie' in the present tense except for 'nosotros' and 'vosotros' forms.
Step-by-step explanation:
The verb preferir is a stem-changing verb in the present tense in Spanish, which exhibits a change from 'e' to 'ie' in its stem. This particular type of conjugation falls under option d. Stem vowel change. Here are the conjugated forms of preferir:
The stem-changing pattern involves the change of the vowel 'e' to 'ie' in the stem of the verb for all forms except nosotros and vosotros. This is a common pattern in Spanish for certain 'ir' and 'er' verbs where the vowel changes when conjugated in the present tense.