Question

3. In order to have their beliefs considered as public opinion, people must _____.

Answer 1

People must express their beliefs and practices. Obviously they're not getting anywhere with their mouth shut and they need to speak their mind and this is the easiest way.
Although its not effective all the time and some people's beliefs are not considered in society but not expressing will be considered as your fault.

Answer 2

In order to have their beliefs considered as public opinion, people must express they're point of view.