Complex sentence: The Hollywood Revue of 1929 was missing Greta Garbo and Lon Chaney, if Lon Chaney and Greta Garbo was in The Hollywood Revue it would have been their first talking features.
Split into simpler sentences: The Hollywood Revue of 1929 was missing Greta Garbo and Lon Chaney. If Lon Chaney and Greta Garbo was in The Hollywood Revue it would have been their first talking features.