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: THE KOREAN WAR 
Clue: In bitter battles of 1951, Pork Chop was a hill & Heartbreak was one of these
[EX A]: ridge

[EX Q]: Category: ALL ABOUT AUTHORS 
Clue: "The Remains of the Day" author Kazuo Ishiguro was a grouse beater for this grandmother of Prince Charles
[EX A]: the queen mother

[EX Q]: Category: NEWTONIAN PHYSICS 
Clue: It's the inward force that a string exerts on a ball whirling on the end of it
[EX A]:
centripetal force