Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.
--------
Question: What currency is used on Christmas Island?

Answer: christmas island


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

Answer: downton abbey


Question: What is the smallest country in Central America Costa Rica, Venezuela or El Salvador?

Answer:
central america