But in some cases,one marketer's owned media become another marketer's paid media —— for instance,when an e-commerce retailer sells ad space on its Web site.词汇：1. in some cases 在某些情况下 2.marketer 市场营销人员 3. owned media 自有媒体 4.become 成为 5.paid media 付费媒体 6.e-commerce 电子商务 7. retailer 零售商 8.sell 销售主干：But in some cases,one marketer's owned media become another marketer's paid media解释说明（可以理解为状语）：for instance,when an e-commerce retailer sells ad space介词短语作后置定语： on its Web site（句中的its回指an e-commerce retailer ）参考译文：但在某些情况下，例如，当一个电子商务零售商出售自己网站的广告空间时，一个营销者的“自有”媒体会成为另一个营销者的付费媒体。句子解说：句中的 when 从句提前译，符合汉语的习惯，值得学习。
