The correct answer is: a person becomes a citizen of another country.
Naturalization is a process that happens to a foreign person after he/she fulfills some requirements established by law in order to become a citizen of another country.
In the United States, for example, a person can apply for naturalization after he/she has been a citizen (must be a green card holder) for at least 5 years and meets other specific requirements. Also, someone who has been born in another country but has American parents and meets the other specific requirements can be eligible for naturalization.
