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 consistency, answers should be in all lower cased letters.
--------
Question: Category: ENVIRONMENTALISM 
Clue: The world's first national park was Yellowstone, opened in 1872; this country opened its first park at Banff in 1887

Answer: canada


Question: Category: ALL ABOUT TROMBONES 
Clue: The most common trombone bears the name of this male singing voice

Answer: tenor


Question: Category: FROG ANATOMY 
Clue: The frog stores liquid waste in this organ & can reabsorb water from it in dry times

Answer:
the bladder