TASK DEFINITION: Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.
PROBLEM: What is the main river of Brazil?

SOLUTION: brazil

PROBLEM: What is the country of origin of the cheese called caerphilly?

SOLUTION: caerphilly cheese

PROBLEM: Who plays Isobel Crawley in the UK television series 'Downton Abbey'?

SOLUTION:
downton abbey