Final answer:
The beginning of the Islamic conquests during the Rashidun Caliphate saw non-Muslims adjusting to Muslim rule due to lower taxes, the defeat and destruction of the Sassanian Empire, and victories over the Byzantine Empire.
Step-by-step explanation:
The correct statement for the beginning of the Islamic conquests during the Rashidun Caliphate is: Non-Muslims adjusted to Muslim rule as the caliphate charged lower taxes relative to the Romans and Persians.
The Muslim armies were successful in defeating and destroying the Sassanian Empire, bringing an end to their rule.
Although there were battles with the Byzantine Empire, the Muslim armies were victorious and not defeated by Heraclius at the Battle of Yarmouk.
Learn more about Islamic conquests during the Rashidun Caliphate