Why Did the Abbasid Caliphate Begin to Decline After Harun

Multiple Choice

Why did the Abbasid caliphate begin to decline after Harun al-Rashid's death?

A) The Abbasids reneged on their promise to appoint Shi'ites to top government positions, so the Shi'ites instigated civil war.
B) The Abbasids embarked on a disastrous campaign to retake northern Africa.
C) A Sunni imam raised questions about the legitimacy of Harun's claims to the caliphate.
D) The caliphs lacked an adequate tax base to support the huge Abbasid army.