<Tr> <Th> Rank </Th> <Th> Airline </Th> <Th> Destinations </Th> <Th> Ref </Th> </Tr> <Tr> <Th> </Th> <Td> American Airlines </Td> <Td> 350 </Td> <Td> </Td> </Tr> <Tr> <Th> </Th> <Td> United Airlines </Td> <Td> 342 </Td> <Td> </Td> </Tr> <Tr> <Th> </Th> <Td> Delta Air Lines </Td> <Td> 322 </Td> <Td> </Td> </Tr>

What are the top airlines in the united states