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: A BUSINESS IS BORN 
Clue: The first drug-store in this chain began operating out of a Chicago hotel in 1901; in 2009 the 7,000th store opened
walgreens

Category: PHILOSOPHY 
Clue: This ancient philosopher wrote about a theory of forms in his "Republic"
plato

Category: DR. WHO... 
Clue: specializes in X-rays & elements, like the one with the atomic number 88 for treating diseases

a radiologist