I believe the answer is B. If you think about D, one cannot simply just live in the country for a few months and be considered a citizen just like that. And C is also inaccurate since there is the right of the soil(which allows anyone born in U.S. territory to be a citizen) and the law of the blood(which allows anyone who has a blood relative living in the U.S. to be legible for citizenship). And how do I explain A... well, there are several tests one needs to pass for naturalization.