(d) Due to trade and cultural exchange
The silk routes enabled not only movement of goods like silk, spices, and precious metals, but also exchange of ideas, religions, and culture between Asia, Europe, and Africa.
Source: Chapter 3, Section 1.1 – Silk Routes Link the World
The passage explicitly states: "Trade and cultural exchange always went hand in hand" on the silk routes. While silk cargoes (a) and gold/silver flow (b) are mentioned, they are only partial reasons. Option (c) is factually wrong — the route linked Asia with Europe and Africa, not Australia. Option (d) best captures the complete reason as stated in the source. In MCQs, always pick the most comprehensive option.