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: INITIALLY YOURS 
Clue: One of the founders of the NAACP was this sociologist & writer of "The Souls of Black Folk"
w.e.b. dubois

Category: THE ELEMENTS 
Clue: Most fluorescent lights are filled with a combination of argon & this element, Kr
krypton

Category: ROCK & ROLL 
Clue: This female vocalist joined Big Brother & The Holding Company in June 1966

janis joplin