Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

[Q]: henan is a province of the people's republic of china.
[A]: henan


[Q]: renty is a commune.
[A]: renty


[Q]: the three-body problem is a problem in the field of physics that experts find interesting.
[A]:
three-body problem