From 1948 to 1961, the proportion of American blacks earning less than $ 3000 a year declined from 78 to 47 percent; at the same time, blacks earning more than $ 10, 000 increased ______ from less than 1 to 17 percent. (proportion)

A．developed by scientists with an interest in genetics
B．useful in explaining some biological phenomena
C．adopted by Hamilton in his research
D．based on animal studies conducted prior to 1930

A．Thus, without the cultural diversity represented by the American South, the culture of colonial America would certainly have been homogeneous in nature.
B．Thus, the contribution of Southern colonials to American culture was certainly overshadowed by that of the Puritans.
C．Thus, convergence, not divergence, seems to have characterized the cultural development of the American colonies in the eighteenth century.
D．Thus, the culture of America during the Colonial period was far more sensitive to outside influence than historians are accustomed to acknowledg