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: DIMENSIONS 
Clue: Don't lose the thread--there are 10 or so dimensions in this physics theory
string theory

Category: GEOGRAPHY 
Clue: This Sudanese capital is located at the junction of the Blue & the White Nile
khartoum

Category: CASTLE LIFE 
Clue: It's usually a body of protective water spanned by the drawbridge

moat