Question: El Retiro is a historic site in Lake Wales, Florida, that since 1970 has been part of a national historic landmark that consists of how many acres of garden?
Sentence (from "Bok Tower Gardens"): Bok Tower Gardens (also known as Bok Mountain Lake Sanctuary and Singing Tower ) is a National Historic Landmark, contemplative garden, and bird sanctuary located north of Lake Wales, Florida, United States.
Relevant evidence: Yes