The best answer is:
D. Adams believed European immigrants had more loyalty to their home countries than to the U.S.
This choice aligns with the context of the Alien Act, which was enacted with concerns over national security and the potential threat that immigrants might pose to the stability and loyalty of the newly formed United States. It reflects a sentiment that immigrants could have divided loyalties, which is a key reason for the act's provisions allowing for the removal of perceived dangerous individuals.