What is the purpose of a topic sentence?

• A. To present evidence.
• B. To summarize the entire essay.
• C. To state the main idea of a paragraph.
• D. To introduce a new topic.

Answer: (C)

The main idea being tested is how a topic sentence sets the focus of a paragraph by naming its central point. The topic sentence states the main idea the paragraph will develop, acting as a guide for the reader and a roadmap for the writer. Everything that follows—examples, details, and evidence—serves to explain or support that idea, keeping the paragraph cohesive and on track with the overall argument or purpose.

Evidence belongs in the sentences that come after, not in the opening line, so presenting evidence is not the function of a topic sentence. Summarizing the entire essay is something a conclusion does, not the opening of a paragraph. Introducing a new topic happens when you move to the next section or paragraph with a transition or a fresh opening, not when you’re presenting the current paragraph’s main idea.