The correct answer is MEXICO.
The National Origins Act was part of the Inmigration Act enacted in 1924, together with the Asian Exclusion Act. The Inmigration Act was a federal law that banned inmigration from Asia, and established a system of quotas in order to regulate the arrival of inmigrants from the Western Hemisphere to the US.
Although the US Border Patrol emerged for the surveillance of the Mexico-US border, Mexicans were still allowed to inmigrate to the US, as they were regarded as a source of cheap labor. However they were charged a $10 tax if they wanted to cross the border.