1. Constantinople was captured in the reign of?

2. Who established the system of public education, including the founding of the University of Baghdad?

3. Who said "If knowledge were suspended from the highest parts of heaven, the Muslims would still strive to reach it"?

4. Who said "I have been sent to perfect good manners"?

5. Which Caliph wrote letter to the Byzantine emperor, in which he invited him to accept Islam or pay tribute to the Islamic Empire?