Database: flight_4

Question: Find the name of airline which runs the most number of routes.
SQL: SELECT T1.name FROM airlines AS T1 JOIN routes AS T2 ON T1.alid  =  T2.alid GROUP BY T1.name ORDER BY count(*) DESC LIMIT 1

Question: Find the busiest source airport that runs most number of routes in China.
SQL: SELECT T1.name FROM airports AS T1 JOIN routes AS T2 ON T1.apid  =  T2.src_apid WHERE T1.country  =  'China' GROUP BY T1.name ORDER BY count(*) DESC LIMIT 1