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: WHAT'S THE BIG IDEA? 
Clue: The 21st century doctrine named for this man allows the U.S. to wage preventive war if an attack on us is coming
george w. bush

Category: ONCE THEY WERE ANGELS 
Clue: She's had a clothing line at K-Mart since 1985
jaclyn smith

Category: BLACK HISTORY 
Clue: This "conductor" usually carried a gun, not a whistle

harriet tubman