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: GENERAL SCIENCE 
Clue: A horse's hooves are made up of this protein, the same protein found in your fingernails
keratin

Category: HOUSEPLANTS 
Clue: Roots sticking through drainage holes in containers are a sign that it's time to do this
re-pot

Category: THE 10 LARGEST COUNTRIES IN THE WORLD 
Clue: The one that spans 11 time zones

russia