Why Did Restrictions on Immigration Increase During the Nineteenth and Early

Why did restrictions on immigration increase during the nineteenth and early twentieth centuries in the United States?

A) Immigration was so low that it wasn't controversial until the latter half of the nineteenth century.
B) Unions gained more power over this time period and were better able to influence policy outcomes.
C) A series of economic crises and depressions led to increasing opposition to immigration.
D) The changing racial composition of the typical immigrant led to different levels of opposition over time.