Answer:
Option A.
All of the following are possible reasons for the decine of the Indus civilization except barbarian attacks
Explanation:
The culture of the Indus Valley was a Bronze Age civilization that developed along the Indus River Valley in Afghanistan, Pakistan and northwestern India. It depended largely on it´s river.
It is believed that the decline of civilization was caused by the drought and decline of trade with Egypt and Mesopotamia. You can also consider the immigration of new peoples, deforestation and floods.