Which Factors Led to the Islamic Conquest of Iran

Which factors led to the Islamic conquest of Iran?

A) The Parsees formed an alliance with the Muslims because of years of persecution under Persian rule.
B) The Sasanian King Chosroes II married the granddaughter of Muhammad which led to a merger between the two groups.
C) Sasanian Persia was in a state of decline caused in part by years of warfare with Byzantium.
D) Most Iranians practiced Zoroastrianism, a peaceful religion; therefore, they refused to engage in battle with the Muslims.