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]: masakuni yamamoto ( , yamamoto masakuni, born april 4, 1958) is a former japanese football player.
[A]: masakuni yamamoto

[Q]: jujutsu (, jujutsu) is an ancient japanese martial art.
[A]: jujutsu

[Q]: the crossbow, or arbalest, is a bow which consists of a bow-like arc called "prod" and cross-wise body called "stock" and trigger mechanism.
[A]:
crossbow