Answer: b. a naturalization application known as the Form N-400.
Although all of these are steps in the naturalization process, the first one that every applicant needs to undertake is the filling of a naturalization application known as the Form N-400. This indicates that the person is interested in applying for naturalization. Naturalization is the process by which a foreign citizen comes to be considered a citizen of the country where he resides, with all the rights and duties that this grants.