The option that best analyzes how trade contributed to cultural change in Southeast Asia in the Medieval era is: "Trade led to the creation of merchant communities, which caused the diffusion of religious practices from Arabia to Southeast Asia."
This response highlights the role of trade in the establishment of merchant networks that not only facilitated economic exchange but also enabled the transfer of cultural and religious ideas, particularly Islam, from Arabia to the Southeast Asian region. The engagement of Arab merchants with local populations often resulted in significant cultural exchange and transformation, making it a key aspect of the cultural change during that period.