What Led to the Growing Concentration of the Working Poor

What led to the growing concentration of the working poor in the "inner cities," while middle-class professionals and business executives increasingly lived further away from
City centers?

A) growing belief in Reform Darwinism and the wish to spread it
B) the increasing number of theaters and restaurants found beyond city limits
C) the lack of jobs in general, not just those that were high paying
D) the growth of transportation options such as streetcars and trolleys
E) mistrust of how safe new, taller apartment complexes were