Final answer:
The correct verb to fill in the blank is 'son'. When the subject is 'ellos', the correct form of the verb 'ser' (to be) in the present tense is 'son'.
Step-by-step explanation:
The correct verb to fill in the blank is son.
When the subject is ellos (they), the correct form of the verb ser (to be) in the present tense is son.
For example, Ellos son de Perú means They are from Peru.
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