Concept:A public demonstration by a group of people is commonly called a protest.
Explanation:The sentence describes aggrieved customers expressing their displeasure openly on the street.
The word “protest” means a strong public statement or action against something considered unfair.
“Contest” suggests a competition, not a street demonstration.
“Argument” is a verbal disagreement and does not fit the idea of a crowd acting together.
“Fight” implies physical combat, which is not indicated by the sentence.
The phrase “staged a fierce protest” is natural and correctly completes the meaning.
Answer:D. protest