Complex sentence: In 1938, the team was hired by Metro-Goldwyn-Mayer to compose songs for "The Wizard of Oz", the most famous of which is "Over the Rainbow," for which they won the Academy Award for Best Music, Original Song.
Split into simpler sentences: In 1938, the team was hired by Metro-Goldwyn-Mayer to compose songs for "The Wizard of Oz". The most famous of these is the song "Over the Rainbow" for which they won the Academy Award for Best Music, Original Song.