Qira'at

With regards to the seven Qira'at of the Quran which reading was the Quran actually revealed in? Sayyed Mohammad Al-Musawi	I understand that the Sunni's believe in seven Ahruf versions of the Quran. Is this true? If so, and while knowing that the Shia don't believe in this idea, does this imply that the Qur'an has not been preserved? Zaid Alsalami
What is the Shi'a understanding of the different Qira'at of the Quran? Why do they exist? What is the difference between these Qira'at and the Sunni belief of seven "Ahruf" of the Quran? Sayyed Mohammad Al-Musawi	Do the Qira’at of the Qur'an have any differences in wording or do they only differ in pronunciation of the words? Sayyed Mohammad Al-Musawi