<Tr> <Td> <Table> <Tr> <Td> </Td> </Tr> </Table> </Td> <Td> </Td> <Td_colspan="2"> Lock E33 (Rochester) </Td> </Tr> <Table> <Tr> <Td> </Td> </Tr> </Table> <Tr> <Td> <Table> <Tr> <Td> </Td> </Tr> </Table> </Td> <Td> </Td> <Td_colspan="2"> East Guard Lock </Td> </Tr> <Table> <Tr> <Td> </Td> </Tr> </Table>

What event made construction of a canal in central america easier apex