I disagree strongly with the solution given on this question, and it seems to go directly against your own "quick lesson" if the answer is "era" -- the time frame is known and relevant because the palace was the home of a king with a specific reign, which would be known. Explícalo, por favor!
In this sentence the timeframe is not seen as relevant. It's just about a building being a palace in the past so we use era. The quiz gave that hint.
Sign in to submit your answer
Don't have an account yet? Join today
Test your Spanish to the CEFR standard