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 BRITISH ISLES 
Clue: This island group that lies just north of the Scottish mainland was known to classical writers as the Orcades
the orkney islands

Category: "TWO" 
Clue: It features Jefferson on the front & the signers of the Declaration on the back
two-dollar bill

Category: MEDICINE & HISTORY 
Clue: Montezuma's real revenge: a 1741 British expedition to conquer Mexico was devastated by this "colorful" disease

yellow fever