His definition of public opinion, the author states that the opinions of private individuals become public opinion when they

I believe the answer is: are openly expressed

Private opinion could only exist in one person's mind,. While it might be provide the most safety and unlikely to cause conflict, it would never be able to change how people think or behave. the second that individual express their opinion to other people, it create a high chance of causing a conflict. But,the chance of other people hearing it and change their opinion  goes up along with it.

well, there are a lot of places we get information about earth from. like science classes, websites, books, newspapers, etc.

the arab empire adopted the muslim religion as their main belief. arabs would influence the people from the territories they invaded towards islam (the muslim belief).

nevertheless, throughout the history of the arab empire, rulers brought intellectual individuals from other religions to their centers of learning. these other foreigners included jews, christians, greeks, persians, and indians.   these resulted in the adoption of important knowledge developed by these cultures by the arabic empire. for example, the works of aristotle were translated from greek to arab and indian scientists brought the numerical concept of "zero" to the arabs.

nowadays, 93% of the arab population is muslim, which at the same time is subdivided in sects including the sunni, zaini, alawi, shia. the remaining 7% is composed mainly of christians.