What happened after the collapse of the Roman Empire, when Christian societies were no longer centers of knowledge?

The correct answer is:

**a. Islamic societies in places like Syria, Persia, and what is now the country of Mali became centers of knowledge.**

After the collapse of the Roman Empire, especially during the early Middle Ages, many classical texts and knowledge were preserved and enhanced by Islamic scholars in various parts of the Islamic world. During this time, Islamic societies became prominent centers of learning, contributing significantly to various fields such as science, mathematics, medicine, and philosophy. Meanwhile, the Byzantine Empire did continue to preserve knowledge, but the statement addresses the broader landscape of knowledge centers that emerged in the Islamic world during this period.