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

Example Input: Which is the only Avril Lavigne song to have reached No.1 in the US Billboard Chart?
Example Output: avril lavigne

Example Input: Which river begins in the Rocky Mountains in south-west Colorado, crosses New Mexico and forms the border between Mexico and the USA before reaching the Gulf of Mexico?
Example Output: new mexico

Example Input: Thereze Bazar and David van Day were better known as which duo?
Example Output:
david van day