What happened to the province of Bithynia and Pontus after the Muslim invasions of the 640s AD?

A. It was reorganized into the Bucellarian, Opsikion, and Optimatoi themes
B. It was reorganized into the Bucellarian, Opsikion, and Optimatoi kingdoms
C. It remained unchanged under the Byzantine Empire
D. It was conquered by the Muslim Empire
Answer: 