The best description of how the Silk Road changed over time is:
a. The Silk Road changed to reflect changing political borders and power structures.
Over the centuries, the Silk Road evolved in response to various factors such as the rise and fall of empires, shifts in political power, and changes in trade practices. As different regions experienced political changes, the routes and centers of trade shifted accordingly. For instance, during the height of the Roman Empire and later the Byzantine Empire, certain routes were prominent, while the Tang and Yuan Dynasties in China facilitated trade through different paths. The conquests of the Mongol Empire in the 13th century temporarily unified vast regions and improved trade through increased safety and stability, but as political dynamics shifted again, trade routes adapted to new realities. Therefore, the Silk Road was not a static entity; it was a dynamic network of trade that transformed in response to historical developments.