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]: the wii u is a video game console that was released by nintendo on november 18, 2012, and is the successor of the wii.
[EX A]: wii u

[EX Q]: a black powder rocket motor pushes a model rocket using black powder.
[EX A]: black powder rocket motor

[EX Q]: yazd province (, "ostan-e yazd" ) is one of the 31 provinces of iran.
[EX A]:
yazd province