Which song is associated with the most popular Disney movie in 1970s?
the most popular movie refers to movie_title where MAX(total_gross); in 1970s refers to (cast(SUBSTR(release_date, instr(release_date, ', ') + 1) as int) between 1970 and 1979);
SELECT T2.song FROM movies_total_gross AS T1 INNER JOIN characters AS T2 ON T1.movie_title = T2.movie_title WHERE CAST(SUBSTR(T1.release_date, INSTR(T1.release_date, ', ') + 1) AS int) BETWEEN 1970 AND 1979 ORDER BY CAST(REPLACE(SUBSTR(T1.total_gross, 2), ',', '') AS float) DESC LIMIT 1