In CASAS Level D, what is the function of "topic sentences" in paragraphs?

• A. They introduce the main idea of the paragraph and guide comprehension.
• B. They provide the concluding summary of the entire passage.
• C. They list all supporting details in order.
• D. They pose questions for the reader.

Answer: (D)

Topic sentences introduce the paragraph’s main idea and set up what the paragraph will explain or argue, which helps you understand its purpose and follow the writer’s train of thought. In CASAS Level D, recognizing this opening idea lets you quickly grasp the focus of the paragraph and anticipate the details that will come next, making the overall reading smoother and easier to track.

The other ideas described don’t fit this role: a concluding summary comes at the end of a passage, not at the start; listing all supporting details happens in the body after the topic sentence; and posing questions is not the essential function of a topic sentence, though a question might appear elsewhere to engage the reader.