Hello. As far as I know, all the Korean grammar books say that when quantity phrases such as 'all of', 'both of', 'some of', 'many of' and so on are used with relative pronoun like 'whom', 'whose+noun' and 'which', 'comma' must be used before them. But I don't think so. Of course, 'comma' before them are used in most of the cases, but I don't think this rule is always applied to all situations like following. 1a. He has three albums, all of which sold over two million copies. b. He has three albums all of which sold over two million copies. 2a. We should eat fresh fruits, most of which offer many vitamins. b. We should eat fresh fruits most of which offer many vitamins. 3a. A reporter visited the regions, some of which are in fear of the mystery. c. A reporter visited the regions some of which are in fear of the mystery. I think (b) version is possible and correct, but just has different meaning with (a) version slightly. Am I right? Thank you always~.