Which category includes individuals seeking entry into the U.S. without citizenship?

The correct choice identifies individuals who are not U.S. citizens and are seeking entry into the U.S. as "aliens." The term "alien" is used in U.S. immigration law to refer to anyone who is not a citizen or national of the United States. This category encompasses various non-citizens, including tourists, students, and workers, who may be classified based on the purpose or duration of their stay.

U.S. nationals refers specifically to individuals who owe allegiance to the United States but are not necessarily citizens, such as individuals born in American Samoa. Immigrants are a subset of non-citizens who have been granted the right to live and work permanently in the U.S.; however, they are already on a path toward citizenship or have that status, which doesn't align with the broader seeking entry context present in the question. Permanent residents are those who have obtained lawful permanent residence status, often holding a green card, which again implies they are not merely seeking entry but have already secured a right to remain in the U.S.

In summary, "aliens" is the most inclusive and appropriate category that accurately describes individuals seeking entry into the U.S. without citizenship.