Answer: Miami está en las costas (shores) del Océano Atlántico.
Step-by-step explanation: The sentence provided can be translated as "Miami is located at the (shores) of the Atlantic Ocean". The word "shore" denotes a piece of land found along the edge of a sea or an ocean. The word in Spanish for "shores" is "costas". Therefore, the word that fills in the blank is "costas" as Miami is effectively a geographic area bounded by a coast.