The correct answer is D) Islam only spread significantly under the Abbasid Dynasty.
The Abbasid dynasty differed from the Umayyad dynasty in that Islam only spread significantly under the Abbasid Dynasty.
One of the biggest differences between the two was their attitude toward Muslim people and non-Muslims. Abbasids accepted non-muslims, while Ummayads did nos accepted conversions. That is why the number of Muslims did not increase during the Dynasty. Another notorious difference is that Abbasids gave priority to the expansion of the culture and knowledge, meanwhile Ummayads focused on military expansion to control other lands.
The other options of the question were A) the Abbasids were more interested in expansion that the Ummayads, B) small, independent states challenged Muslim rule under the Ummayad Dynasty only, and C) the Bbasi government was more directly connected to the Islamic religion.