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: What is the capital city of Colombia?
Example Output: colombia

Example Input: In the SI system, what is the basic unit for the measurement of electric current?
Example Output:
electric current