The statement that describes a relationship of causation rather than correlation is:
A. Because of trade along the Silk Road, Buddhism spread throughout Asia.
This statement shows a cause-and-effect relationship. It explains that the trade along the Silk Road led to the spread of Buddhism throughout Asia. The trade provided a means for the exchange of ideas, culture, and religion, which facilitated the spread of Buddhism to different regions along the Silk Road. This exemplifies causation as the trade activity directly influenced the diffusion of Buddhism across Asia.
On the other hand, statements B, C, and D do not illustrate causation but rather provide information or facts related to the Silk Road without showing a direct cause-and-effect relationship between different events or phenomena.