Which is the most fuel efficient car in 1975?
car's name refers to car_name; the most fuel efficient refers to max(mpg); in 1975 refers to model_year = 1975
SELECT T1.car_name FROM data AS T1 INNER JOIN production AS T2 ON T1.ID = T2.ID WHERE T2.model_year = '1975' ORDER BY T1.mpg DESC LIMIT 1