You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: THE PRESIDENTIAL CABINET 
Clue: 7 women have been the secretary of this, the most for any department in the president's cabinet
labor

Category: TRAINS 
Clue: As of 2006, you can take a 48-hr. ride between these 2 cities, with a stretch on the world's highest railroad
beijing & lhasa

Category: THE SUPREME COURT 
Clue: 2 of the 3 current Supreme Court justices appointed from the D.C. Court of Appeals

ruth bader ginsburg, antonin scalia & clarence thomas