Why is Narutos body chosen to lock up kyuubi?
The fourth hokage (naruto’s father) sealed the kyuubi inside naruto’s body. Kyuubis are strong and possess an incredible power. If the kyuubi is sealed inside a human’s body, the person who possess that kyuubi will be called Jinchuriki. In this case, if the jinchuriki (like naruto) controls the kyuubi inside his body, he can be a great and powerful person. So naruto’s father (4th hokage) sealed the 9 tailed fox to his son’s body in exchange for his life, because he believe that naruto can be a great jinchuriki. Maybe you read the manga series of naruto so u can understand the full story.