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.

[EX Q]: emiliano zapata salazar (august 8, 1879 april 10, 1919) was a leader in the mexican revolution, which started in 1910.
[EX A]: emiliano zapata

[EX Q]: nexon corporation is a korean gaming corporation and developer of online games and mmorpgs.
[EX A]: nexon

[EX Q]: a surfactant is a chemical that lowers the surface tension of a liquid.
[EX A]:
surfactant