What can an increase in the power of the Ku Klux Klan during the 1920s be attributed to?

What can an increase in the power of the Ku Klux Klan during the 1920s be attributed to?

a) a rise in nativism and the Great Migration
b) a rise in nativism and the passage of the Nineteenth Amendment
c) a rise in immigration of northern and eastern Europeans
d) the Great Migration and the passage of the Nineteenth Amendment