Final answer:
The correct verb to complete the sentence is 'están'.
Step-by-step explanation:
The correct verb to complete the sentence is están. Carolina y su hermana are referred to in the third person plural, so we need a verb that agrees with that subject. The verb están is the conjugation of the verb estar used for third person plural subjects. It indicates a temporary state or conditions, which fits the context of the sentence where Carolina and her sister are nervous about an interview tomorrow.
Learn more about Spanish verb conjugation