The correct answer is C. editorial.

Explanation:
In this context, "leader" refers to an article or opinion piece in a newspaper, often called an "editorial." This is a piece that expresses the newspaper's views or commentary on a particular issue, in this case, inflation.

- A. president: This refers to a political leader, not a newspaper article.
- B. headline: A headline is the title of a news story, not an opinion piece.
- C. editorial: This is correct. An editorial is a type of article that reflects the views or opinions of the publication on a particular issue.
- D. columnist: A columnist writes regularly for a newspaper but doesn't necessarily represent the publication's views on a particular topic.
- E. proprietor: A proprietor is the owner of a business, which is unrelated to the meaning of "leader" in this context.

Therefore, C. editorial is the best option.