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.

Category: SALAD DRESSING 
Clue: This national-named dressing often made with ketchup is found in deli sandwiches
russian dressing

Category: ENVIRONMENTALISM 
Clue: The world's first national park was Yellowstone, opened in 1872; this country opened its first park at Banff in 1887
canada

Category: MEDICAL ABBREV. 
Clue: A fat & cholesterol-carrying molecule: LDL

low density lipoprotein