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]: a commode is a special piece of furniture.
[EX A]: commode

[EX Q]: the cyclostomes (or cyclostomata) are the lamprey and hagfish.
[EX A]: cyclostome

[EX Q]: sitting bull (about 1831 – december 15, 1890), real name tatanka yotanka, was the chief of a native american tribe called hunkpapa-lakota-sioux.
[EX A]:
sitting bull