Complex sentence: Rita Moreno was dubbed by Betty Wand in the song "A Boy Like That" because the song was in too low for her, but Moreno sang her own vocals in "America".
Split into simpler sentences: Rita Moreno was dubbed by Betty Wand in the song "A Boy Like That" because the song needed to be performed at a register that was too low for her. However, Moreno sang her own vocals in "America".