<Tr> <Td> </Td> <Td> 11 </Td> <Td> 39.155 </Td> <Td> </Td> </Tr> <Tr> <Td> 2005 </Td> <Td> 14 </Td> <Td> 49.090 </Td> <Td> </Td> </Tr> <Tr> <Td> 2006 </Td> <Td> 14 </Td> <Td> 49.250 </Td> <Td> </Td> </Tr> <Tr> <Td> 2007 </Td> <Td> 21 </Td> <Td> 61.600 </Td> <Td> </Td> </Tr>

What are the three characteristics of the great wall of china