D. A topic sentence is the central idea of a paragraph, while a main idea is the central idea of an entire text
This is the correct answer. The main idea is the central idea of a text. In an essay the central idea is what the entire essay is about. This can be found in the thesis statement. The thesis statement is found in the introductory paragraph and states the main idea of the essay. The topic sentences can be found near or at the very beginning of each body paragraph. They relate directly to the main idea and introduce a supporting idea.