Answer:
Roberto vive en Puerto Rico.
Step-by-step explanation:
There are different possibilities to complete this phrase. The important thing to bare in mind is that you need a verb to fill in this gap in order to follow the standard structure of a sentence: Subject + Verb+ Complement.
Roberto vive en Puerto Rico.
(subject) (verb) (complement of place)
The preposition "en" is also required, after the verb "vive", to introduce the complement "en Puerto Rico" (also called adjunct of place). The verb "vive" is conjugated in the present of the 3rd person singular, as the subject is "Roberto."
Note: The verb can be conjugated in different tenses (but always in the 3rd person singular) , for instance, Roberto vivió en Puerto Rico is also correct.
Another option to complete this phrase could be "Roberto es de Puerto Rico", which indicates place of origin. It is also correct as it follows the structure-: Subject + Verb + Complement. The verb must be conjugated in the 3rd person singular, in this case "es".