<Tr> <Th> By era </Th> </Tr> <Tr> <Td> <Ul> <Li> Han </Li> <Li> Tang </Li> <Li> Song </Li> <Li> People's Republic <Ul> <Li> Agriculture </Li> </Ul> </Li> </Ul> </Td> </Tr> <Ul> <Li> Han </Li> <Li> Tang </Li> <Li> Song </Li> <Li> People's Republic <Ul> <Li> Agriculture </Li> </Ul> </Li> </Ul> <Li> People's Republic <Ul> <Li> Agriculture </Li> </Ul> </Li>

Which inventions had the greatest impact on trade in china during the middle ages