How far north did islam spread in the 600's? how far east?

In the 600's, Islam spread far North and East Africa through trade and the spread of the Arabic language. The expansion of the Arab Empire in the years following the Prophet Muhammad's death led to the creation of caliphates, occupying a vast geographical area and conversion to Islam was boosted by missionary activities particularly those of Imams, who easily intermingled with local populace to propagate the religious teachings.

Ithink the answer is b : )