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: WHAT SHOULD I "DU"? 
Clue: A philosophical system that seeks to explain all phenomena in terms of 2 distinct principles
dualism

Category: CLASSICAL MUSIC 
Clue: Mendelssohn's "Songs without Words" were once the most popular pieces for this instrument
piano

Category: GENERAL SCIENCE 
Clue: It's the "specific" ratio between the density of pure water & that of another substance; for gold, it's 19.3

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
specific gravity

