The correct answer is - C) immigration from largely Catholic countries such as Mexico.
Throughout the past decades, there were lots of people from the countries from Latin America that migrated into the United States. They are mostly Catholics. Also, these populations tend to have a bigger fertility rate, but also tend to be much more religious too. The majority white population, that is Catholic in general, has a low fertility rate, but also there's a big increase in atheists and agnostics, so the percentage of Catholic Christians that are white constantly falls down, while the Latino Catholic Christians are rising in number and percentage.
