Which of the Following Statements About Social Mobility Is Correct

Which of the following statements about social mobility is correct?

A) There are possibilities for social mobility within class systems,although there are also constraints to mobility.
B) Open class systems allow mobility for all individuals from one class to another depending on their work ethic and the historical time period.
C) Class systems do not support social mobility,although some limited mobility does occur under certain circumstances.
D) Social mobility does not occur within a stratified society.
E) Social mobility does not occur openly within any complex society,although there is suppressed movement in and out of the middle class.