Final answer:
The correct verb form that completes the sentence is 'habló'.
Step-by-step explanation:
The correct verb form that completes the sentence is habló.
Since the subject of the sentence is 'mi hermana' which is a singular third-person pronoun, the appropriate verb form should also be singular and in the third-person. In this case, 'habló' is the correct form in Spanish for 'he/she spoke' which matches the subject 'mi hermana'.
For example, you can say 'Mi hermana habló conmigo anteayer por teléfono' which translates to 'My sister spoke to me on the phone the day before yesterday'.
Learn more about Spanish Verbs