TASK DEFINITION: Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.
PROBLEM: Who has taken over the TV role of Doctor Who, from actor David Tennant?

SOLUTION: doctor who

PROBLEM: In which Indian city is Eden Gardens, the second largest test cricket ground in the world?

SOLUTION: eden gardens

PROBLEM: The Kalahari Desert in Africa stretches across South Africa, Botswana and which other country?

SOLUTION:
botswana