Identify the scenario that demonstrates the process of cultural diffusion.
a. a farmer growing crops on a cultivated plot of land
b. the spread of illness from animal-borne diseases
c. the development of a writing system
d. a merchant traveling to sell his goods in another society

The best scenario for the process of cultural diffusion is the following:
 
a merchant traveling to sell his goods in another society

the first two options are not even relating to culture, and while the third one is, it is not a cultural diffussion, but a development that could have happened in one culture only.

Ithink the answer is d but don’t answer it. i need points.