Final answer:
Public opinion is the aggregation of individual views on an issue. It is a collection of popular views that are not always based on facts and can be influenced by various factors. Pressure groups use organized efforts to shape public opinions.
Step-by-step explanation:
Public opinion is the aggregation of individual views that represent the feelings that people hold on an issue at a given point in time. It is a collection of popular views about something, such as a person, an event, or an idea. Public opinions are not always based on facts as they can be influenced by personal experiences, beliefs, and biases. Pressure groups do use organized efforts to shape public opinions by promoting their causes through various means. However, public opinions are not measured by experts but are instead obtained through methods like public opinion polls.