The trust's eye unit is believed to be one of only 10 national eye retrieval centres.
You can buy it in the Pebble Beach pro-shop, one of only two retail outlets.
Constructed in 1914, it is one of only 200 vessels in the National Historic Fleet.
It is one of only two shipping companies based in Cardiff, employing 275 people.
Kennedy was one of only six senators in U.S. history to serve more than 40 years.
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Lindsey Vonn has won four Overall World Cup titles, one of only two women in history.
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The islands are also one of only two locations in England where Manx shearwaters breed.
The latter is one of only four in the nation with Giant pandas, a major draw.
Komodo Island is also distinguished by its pink sand beach, one of only seven in the world.
Mr McKnight, who managed to climb into a lifeboat, was one of only 44 people who survived.
Power and Associated 2012 Customer Service Champion and is one of only 50 U.S. companies so named.
Howard is also one of only three players who will guarantee their team a spot in the playoffs.
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The same can be said for one of only two 2nd round running backs, LaMichael James from Oregon.
The city is one of only two sites to host the exhibition which depicts Lowry's visions of Britain.
Ninewells is one of only three places in the UK to offer the specialised surgical and chemotherapy procedure.
McLaren, one of only two teams still using the energy power-boost system, suffered a poor start to 2009.
Colston Bassett has one of only five dairies, located in Derbyshire, Nottinghamshire and Leicestershire, licensed to produce Blue Stilton.
Oncology is one of only a handful of disciplines whose practitioners buy drugs and administer them in their offices.
Incongruously, Industry housed one of only two public golf museums in the country.
He is one of only 10 players who have played more than 50 games for the 1996 Africans champions.
He was one of only 10 Democrats in 1991 who voted to go to war in the Persian Gulf.
Apparently his grandfather was one of only four white people in town who would do business with African Americans.
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In 2004 Texas became one of only four states in America where whites are no longer in the majority.
Louis is one of only two cities left in America that does not operate its own public safety department.
His daughter is one of only a few dozen youngsters left in town.
On paper Albania is one of only a few European countries that did not see its economy shrink last year.
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This horde surpasses the gross domestic product of Germany, one of only six nations to have fewer billionaires this year.
Newcastle Turkish Baths on Northumberland Road opened in 1928 and is one of only 11 Victorian Turkish baths in England.
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