What Events During the Early Portion of the Twentieth Century

What events during the early portion of the twentieth century in the United States are referred to as the "Great Migration"?

A) a large influx of Chinese immigrants from San Francisco to Los Angeles
B) movement of African Americans from southern to northern U.S. cities
C) a large portion of Jewish Americans moving into suburbs around major cities
D) movement of Mexicans into border towns in southern Texas
E) none of these