Why Were American Suburbs of the 1950s So Heavily Segregated

Why were American suburbs of the 1950s so heavily segregated?

A) African-Americans pREFerred to live in the inner cities.
B) Neighborhoods formed around churches, and as long as churches were segregated, suburbs would remain so as well.
C) All states had laws in place mandating the segregation of residential districts.
D) Residents, brokers, and realtors dealt in contracts and mortgages that barred sales to nonwhite residents.
E) The federal government required segregated residential neighborhoods.