Could someone please explain the answer to this question?

If trade in the ancient to early modern era (from 4000 BC to 1870 AD) could be described by classical models of cross-country differences in labour productivity, resource endowments and other factors, and post-WWII trade could be characterized increasingly by external and internal economies models of trade, then what would best characterize Global Value Chains: C) Horizontal fragmentation models. C) Horizontal fragmentation models C) Vertical fragmentation models. C) Network economies. C) Gravity models.