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Question: When critical altitude is sea level, what is the compression ration for a supercharger gear ratio of 7:1?
Columns: ['Engine', 'Power, continuous', 'Critical altitude This is the highest altitude at which the engine can achieve its full continuous power rating. Above this altitude, power falls off with height as with a naturally aspirated engine . See Supercharger#Altitude effects for details.', 'Power, takeoff', 'Compression ratio', 'Supercharger gear ratio', 'Octane rating', 'Dry weight']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Wasp Jr. A', 'hp (kW) at 2,000 RPM', 'sea level', 'same', '5.0:1', '7:1', '68', 'lb (kg)']
SQL:

assistant: SELECT "Compression ratio" FROM "Table" WHERE "Critical altitude This is the highest altitude at which the engine can achieve its full continuous power rating. Above this altitude, power falls off with height as with a naturally aspirated engine . See Supercharger#Altitude effects for details." = 'sea level' AND "Supercharger gear ratio" = '7:1';