<Tr> <Th> Urban </Th> <Td> 2,122.8 sq mi (5,498 km) </Td> </Tr> <Tr> <Th> Metro </Th> <Td> 10,874 sq mi (28,160 km) </Td> </Tr> <Tr> <Th> Elevation (mean) </Th> <Td> 594 ft (181 m) </Td> </Tr> <Tr> <Th> Highest elevation--near Blue Island </Th> <Td> 672 ft (205 m) </Td> </Tr>

Which of the following was the largest us industry in the 1920s