In nonfiction, which of the following best describes the role of a topic sentence in a paragraph?

• A. It states the central idea of the paragraph.
• B. It lists supporting details.
• C. It introduces a new tangent.
• D. It is optional.

Answer: (A)

In nonfiction writing, a paragraph centers on one main idea, and the topic sentence states that idea and sets the point the rest of the paragraph will support with details, evidence, and examples. This upfront focus helps readers know what the paragraph is about and how the following sentences will fit together to explain or prove the idea.

Listing supporting details is what the other sentences do to develop the idea, not the function of the opening line itself. Introducing a new tangent would derail the paragraph from its main point, breaking coherence. While some writers experiment with structure, the topic sentence is not generally optional in nonfiction; it anchors the paragraph and keeps it on track.

So the best choice is that the topic sentence states the central idea of the paragraph.