<Tr> <Td_colspan="1"> Eastern Jin </Td> <Td_colspan="7"> Sixteen Kingdoms </Td> </Tr> <Tr> <Td_colspan="8"> Northern and Southern dynasties 420--589 </Td> </Tr> <Tr> <Td_colspan="8"> Sui dynasty 581--618 </Td> </Tr> <Tr> <Td_colspan="8"> Tang dynasty 618--907 </Td> </Tr>

Which of the following is enforced by the chinese government as a means to control information