The document discusses topic sentences and body paragraphs. It defines topic sentences as sentences that introduce the subject of a paragraph and convey its organization and content. Effective topic sentences unify the paragraph and support the thesis statement. Topic sentences should be placed at the beginning of the paragraph, though sometimes a transitional sentence may precede it. Topic sentences act as "mini-theses" and contain a topic and controlling idea. Using clear topic sentences allows writers to stay focused and helps readers understand the paragraph.