Answer:
A stem is the part of the verb that comes before the ending (which, in infinitive verbs, is always either ar, er, or ir). In regular conjugations, the stem doesn't change, where in irregular conjugations, it can be completely different. In stem-changing verbs, the change is in the last vowel of the stem.
Explanation:
Esa música no me gusta, prefiero esta.
So your answer is B. esta
