Final answer:
(C) Most people are Persian and the majority religion is Shia Islam.
Most Iranians are Persian and follow Shia Islam. This aligns with Iran's ancient history and its choice in the 16th century to adopt Shia Islam as the state religion.
Step-by-step explanation:
The statement about the ethnicity and religion of Iran that is true is: Most people are Persian and the majority religion is Shia Islam. Iran has a significant Persian heritage, tracing back to the ancient Persian Empire, and most of its population identifies as Persian, not Arab.
As for religious practices, most Iranians follow Shia Islam, unlike many of their Sunni-majority Muslim neighbors in the Middle East. This distinction in religious tradition dates back to the early 16th century when the Persian Empire declared Shia Islam as its official religion.
This decision marked a divergence from the surrounding predominantly Sunni regions, which has implications for regional dynamics to this day.