As it is presented in the passage, rather than a smooth progression the development of the human character and personality is a series of ______.

A．Slaves in Greece in the sixth century
B．
C．were not politically significant.B. The "burghers" of the later Middle Ages constituted an entirely new social class.C. To some extent, social mobility can be attributed to the growth of trade.
D．The new class made up of traders and executive officials of the later Middle Ages made the development of a money economy possibl

A．the conflicts between the peasants and the landed aristocrats
B．the foreign residents
C．slaves
D．the newly emerging middle class in the sixth century