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.

[EX Q]: Category: CORPORATE AMERICA 
Clue: Every year, this company delivers more than a billion packages, more than the Post Office
[EX A]: ups

[EX Q]: Category: DIMENSIONS 
Clue: Don't lose the thread--there are 10 or so dimensions in this physics theory
[EX A]: string theory

[EX Q]: Category: RUSSIAN HISTORY 
Clue: In 1240 his grandson Batu invaded Kiev & Russia became part of the Mongol empire
[EX A]:
genghis khan