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"What'll I Do" was used as the theme song for "The Great Gatsby" 1974
The Exorcist
Barry Manilow
The instrument used in the Doctor Who theme tune is the theremin.
The musical score for ET was written by John Williams (the composer-conductor, not the classical guitarist of the same name).
A leitmotif is any repeated musical theme in a film, so that could be what you're looking for. :)
"What'll I Do" was used as the theme song for "The Great Gatsby" 1974
The Exorcist
It isn't any musical; it's just a commercial but it has the same theme as the Disney movie Mary Poppins.
"The Pink Panther Theme" is the song to the movie, and Henry Mancini is the musical genius behind it.
The musical instruments in the charmed theme song are the bass guitars and saxophones.
high school musical 3
complete
complete
Why not do a movie/ musical theme? They can swim to the music from grease, fame, wicked and even footloose...
symphonic poem
By this question, I am assuming that you mean the opening music in the 1956 musical with Yul Brynner and Deborah Kerr. As was done on the broadway stage, the movie opened with an Overture, which presented several of the musical motifs from the soundtrack.