They (as in the poor and lower class) began to question the rights of the Caliphs to be ruling/guiding them. There was negligence in the government and no one was running it properly allowing for the Turks to gain the upper hand causing riots not to mention Muslims and non Muslims were clashing ideas. The empire got to big and out of hand for anyone to control.
D.
Because the author can show how characters change (A), but they need to show how the characters acted before the change (C). And B is just what explains the character.
The benefit is that OPEC coordinates petroleum policies of its member countries which stabilizes the oil markets. Stable oil markets benefits the world economy. Drawbacks include limitations in actual power in terms of controling member countries and actual prices.
Answer:
Food, population and leaders