Answer: A thesis statement
Explanation: Every paragraph must include an introduction as well as a thesis statement. A thesis statement usually appears at the end of the introductory paragraph of a pAper and offers a summary of the main idea of a research paper or essay. A thesis statement is usually a sentence that explain the main point of an essay.
Therefore, every paragraph must have an idea or message its passing across, A thesis statement is the one sentence that will pass summarize the message of the paragraph to the reader.