What is the primary purpose of the topic sentence in a paragraph?

• A. To present a detailed example within the paragraph.
• B. To conclude the entire passage.
• C. To introduce the main idea of the paragraph and guide comprehension.
• D. To emphasize the author's opinion about the topic.

Answer: (C)

The main idea being tested is that the topic sentence introduces the paragraph’s main idea and guides what comes next. A strong topic sentence signals the focus of the paragraph, helping readers anticipate and understand the details, examples, and explanations that follow. For example, a paragraph about the benefits of daily exercise might start with a sentence like, “Regular physical activity improves energy, mood, and overall health,” which sets up the specific points that will be discussed in the rest of the paragraph. That alignment–introducing the main idea and directing comprehension–is why this choice fits best.

Why the other ideas don’t fit as well: a detailed example is usually presented in the supporting sentences, not in the opening line; concluding the entire passage belongs to the final part of the text; and while a topic sentence can express a viewpoint in persuasive writing, its primary job is to present the paragraph’s main idea and shape the reader’s understanding.