instruction:
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 consistency, answers should be in all lower cased letters.
question:
Category: AROUND THE U.S.A. 
Clue: Any Texan can tell you that this city is "Big D"
answer:
dallas


question:
Category: TRANSPORTATION 
Clue: In the 19th century Gustavus Swift developed this type of railway car to preserve his packed meat
answer:
refrigerator car


question:
Category: SCIENCE GUYS 
Clue: Eugene Dubois died in 1940 still believing his "Java Man" to be this legendary connector between man & ape
answer:

the missing link