What is the 23rd letter of the 24-letter Greek alphabet?

23 years after the United States did so, Brazil abolished what in 1888? About 23,000 casualties were suffered at the Civil War battle of Pittsburg Landing, also known by what name? The presidential library at 2313 Red River Street in Austin, Texas, is dedicated to which president? Casino magnate Sheldon Adelson opened his $1.9 billion Palazzo resort in which city in 2007? Which actor is the father of "24" star Kiefer Sutherland? Which Chaucer masterpiece links 24 tales told by pilgrims? U.S. Route 1, about 2,400 miles long, runs from Fort Kent in which state all the way down to Florida? Which band, 25 years after breaking up, had a No. 1 album in late 1995?