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: IMPOSSIBLE 
Clue: (AUDIO Daily Double):  Impossible as it may sound, '60s sitcom star heard here:  "To dream, the impossible dream, to fight the unbeatable foe...."
jim nabors

Category: THE NEW YORK TIMES SCIENCE TIMES 
Clue: Scholars can't read a 10-word column found in Guatemala but know it means these people had writing in 2300 B.C.
the mayans

Category: THE MIDDLE AGES 
Clue: In 762 Al-Mansur established this city on the Tigris River as the capital of the Abbasid Caliphate

baghdad