Complex sentence: With 10 million copies sold worldwide, his soundtrack to Once Upon a Time in the West is one of the best-selling instrumental soundtracks worldwide, while his scores for The Good, the Bad and the Ugly and The Mission are both certified Gold by RIAA.
Split into simpler sentences: With 10 million copies sold worldwide, his soundtrack to Once Upon a Time in the West is one of the best-selling instrumental soundtracks worldwide. His scores for The Good, the Bad and the Ugly and The Mission are both certified Gold by RIAA.