How many people moved across borders to become permanent residents of Western Europe from the 1960's through the 1980's

A．The movement from rural to urban areas.
B．The movement from urban to rural areas.
C．The movement from Europe to America.
D．The movement from Africa to America.

A．the largest mass expulsions have been those imposed by Nazi Germany
B．the largest slave migrations were compelled by European slave traders
C．the largest migration in history has been called the Great Atlantic Migration
D．between World War I and II, about 6 million people migrated to Europe