Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.

Ex Input:
What is the name of the main thoroughfare in Barcelona, which runs from the Placa de Catalunya to the sea?

Ex Output:
barcelona

Ex Input:
The Byzantine Empire is the term used since the 19th century to describe the Roman Empire of the Middle Ages, centred on its capital, where?

Ex Output:
byzantine empire

Ex Input:
Which Australian city shares its name with the wife of William IV?

Ex Output:
australia