TASK DEFINITION: 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.
PROBLEM: Category: PHOTOGRAPHERS 
Clue: In April 1875 the Library of Congress gained possession of his Civil War photographic plates for $25,000

SOLUTION: mathew brady

PROBLEM: Category: DOUBLE TALK 
Clue: In the 1920s Donald Duncan introduced this child's toy to America & it's had its ups & downs ever since

SOLUTION: yo-yo

PROBLEM: Category: 4.O 
Clue: One is filled with pupils

SOLUTION:
a schoolroom