Respuesta :
The correct answer is C. around forts; modifies were built.
In this sentence, the phrase âaround fortsâ is functioning as an Adverb Phrase since it is giving information about where the cities were built, that is to say, it is an adverb of place. Furthermore, the Adverb Phrase is modifying the Verb Phrase âwere builtâ as it is a post-modifier. Â