Who was the first Abbasid caliph of Islam?

A. Abu Ja’far al Mansur
B. Abu al-Abbas al-Saffah
C. Abū ʿAbd Allāh Muḥammad (Al Mahdi)
D. Abū Muḥammad Mūsā (Al Hadi)

Submitted by: Syed Amjad Ali Naqvi