Question: Which of the lower keys is served by the bridge that crosses over the Pigeon Key Historic District?
Context: Money Key is a small island in Monroe County in the unincorporated, Lower Florida Keys (not to be confused with Little Money Key or Melody/Mystery Key).  It is located in the Atlantic Ocean between Little Duck Key (formerly known as "Big Money Key") and Pigeon Key. The Perdido Key Historic District is a U.S. historic district (designated as such on March 10, 1980) located southwest of Warrington, Florida.  The district is a 6 acre section on the eastern tip of Perdido Key.  The area was formerly a separate islet known as Foster's Bank, where Fort McRee was built. Pigeon Key is a small island containing the historic district of Pigeon Key, Florida.  The 5 acre island is home to 8 buildings on the National Register of Historic Places, some of which remain from its earliest incarnation as a work camp for the Florida East Coast Railway.  Today these buildings serve a variety of purposes, ranging from housing for educational groups to administrative offices for the non-profit Pigeon Key Foundation.  The former Assistant Bridge Tender's House has been converted into a small museum featuring artifacts and images from Pigeon Key's colorful past.  It is located off the old Seven Mile Bridge, at approximately mile marker 45, west of Knight's Key, (city of Marathon in the middle Florida Keys) and just east of Moser Channel, which is the deepest section of the 7 mi span. The Pigeon Key Historic District is a U.S. historic district (designated as such on March 16, 1990) located on Pigeon Key in Florida.  The district is off U.S. 1 at mile marker 45.  It contains 11 historic buildings and 3 structures.  Although the old Seven Mile Bridge crosses over the island, it and its exit ramp to the island were closed in 2008.  Since then, access has been by ferry or private watercraft only, but in 2014 FDOT approved a $77 million plan to restore it. The Seven Mile Bridge is a famous bridge in the Florida Keys, in Monroe County, Florida, United States.  It connects Knight's Key (part of the city of Marathon, Florida) in the Middle Keys to Little Duck Key in the Lower Keys.  Among the longest bridges in existence when it was built, it is part of the Overseas Highway in the Keys, which is part of the 2,369-mile U.S. Route 1. The Dry Tortugas are a small group of islands, located in the Gulf of Mexico at the end of the Florida Keys, United States, about 67 mi west of Key West, and 37 mi west of the Marquesas Keys, the closest islands.  Still further west is the Tortugas Bank, which is submerged.  The first Europeans to discover the islands were the Spanish in 1513, led by explorer Juan Ponce de León.  They are an unincorporated area of Monroe County, Florida, and belong to the Lower Keys Census County Division.  With their surrounding waters, they constitute the Dry Tortugas National Park. The Marquesas Keys form an uninhabited island group about 20 miles west of Key West, 4 miles (6 km) in diameter, and largely covered by mangrove forest.  They are an unincorporated area of Monroe County, Florida and belong to the Lower Keys Census County Division.  They are protected as part of the Key West National Wildlife Refuge.  The Marquesas were used for target practice by the military as recently as 1980. Pigeon Key is a historic district located on the small island of Pigeon Key in the lower Florida Keys, United States.  The island is named "Cayo Paloma" on many old Spanish charts.  It is located off the old Seven Mile Bridge, at approximately mile marker 45, west of Knight's Key, (city of Marathon in the middle Florida Keys) and just east of Moser Channel, which is the deepest section of the seven-mile span. The Harrisburg Covered Bridge (also called Pigeon River Covered Bridge, East Fork Bridge or McNutts Bridge) is a historic covered bridge in Sevier County, Tennessee, in the United States.  It is located east of Sevierville off U.S. Highway 441.  The bridge is a king post truss design and crosses the East Fork of Little Pigeon River. The Boca Chita Key Historic District is a U.S. historic district within the Biscayne National Park in Miami-Dade County, Homestead, Florida.  Located on the northwest section of Boca Chita Key, delimited by Biscayne Bay in the north and west and a half ruined stone wall on its southern side, it contains three historic buildings and the Boca Chita Lighthouse.  On 1 August 1997, it was listed in the National Register of Historic Places for its architectural, historical and recreational values.
Answer: Little Duck Key