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: FILTHY RICH 
Clue: Worth over $15 billion, Robson, son of Sam, runs this company, the USA's largest private employer
answer:
wal-mart


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: WHAT A "CARD"! 
Clue: It's a paperboard sign carried by a picketer
answer:

a placard