Final answer:
The correct word to complete the sentence is 'son'. 'Son' means 'are' in Spanish.
Step-by-step explanation:
The correct word to complete the sentence is son. 'Ustedes' is the Spanish pronoun for the second-person plural 'you all'. When referring to multiple people, the verb form used is 'son', which means 'are'. For example, the sentence 'Ustedes son alumnos de español, ¿no?' translates to 'You all are Spanish students, right?'
Learn more about Using the correct verb form in Spanish sentences