The correct answer is B) The Ottomans and Safavids often went to war with each other over issues of leadership.
A major source of conflict between the Ottoman and Safavid empires was "The Ottomans and Safavids often went to war with each other over issues of leadership."
It is common to see in history how dominant empires waged war with other empires for the issue of power and control. That was the case of the Ottoman Empire and the Safavid Empire. There were armed conflicts such as the Battle of Chaldiran (1514), in which the Ottomans won and conquered Eastern Anatolia and parts of Northern Iran. Both territories were annexed to the Ottoman Empire. The Safavid Empire reacted with a series of attacks in the following years for the control of the borders. Both Empires finally signed the Treaty of Zuhab on May 17, 1639.
The other options of the question were A) Most inhabitants of one empire were Shi'a Muslims and most of the other empire belonged to the Sunni branch of Islam. C) Each empire wanted to control the trade between the Muslim world, Africa, and East Asia. D) The two empires competed for territory in western Europe.