Concept:A referendum is a direct method used to measure public opinion on a specific issue.
Explanation:Public opinion is the collective view of citizens on matters of public interest.
A referendum allows the electorate to vote for or against a particular law or policy.
Through the votes cast, the government obtains a clear aggregate view of what the people want.
This makes referendum a reliable tool for measuring public opinion.
Other recognised methods include elections, opinion polls or surveys, direct observation, and analysis of mass media content.
Negotiation is a bargaining process, strike action is a form of protest, and rumour is unverified information, none of which measures public opinion accurately.
Answer:C. Referendum