A topic sentence is designed to express the central idea or subject matter of a paragraph, providing the reader with a clear focus on what the paragraph will discuss. Therefore B is the correct answer. * **Core concept**: Understanding the purpose of a topic sentence in paragraph structure. * **Solution analysis**: The topic sentence is at the beginning and establishes the theme. Thus, option B is the only one that aligns with the purpose of a topic sentence. * **Option A Analysis**: Incorrect because supporting evidence comes after topic sentence. * **Option C Analysis**: Incorrect because a conclusion is at the end of the paragraph. * **Option D Analysis**: Incorrect because new topics belong in new paragraphs. * **Easy mistake**: Confusing the purpose of different parts of a paragraph.