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

Which English king was the son of Edward, the Black Prince?
edward, the black prince

Chep Lap Kok airport is located where?
hong kong international airport

Which American philosopher built a hut near Walden pond, Concord in 1845, and lived there as a hermit for a few years?

concord