Answer:
A: By conquering and expanding.
Step-by-step explanation:
Cultural diffusion is the phenomenon of the spreading and belief in the social, cultural, and even the religious activities of one culture by another. basically, one culture's influence over another is known as cultural diffusion.
The Roman Empire was one of the most successful empires in the history of the world. And cultural diffusion also happened on a large scale due to the expansion and conquering of other lands. Whatever lands they conquered was joined by easy-access roads through which the Roman culture was spread.
Thus, the correct answer is option A.