The right answer is "none of the above".
There is no exact number of how much evidence the central idea of a paragraph needs, it will depend on what is being written. In fact, it is not the number of sentences that a paragraph puzzles, but the unity and coherence of ideas between these sentences that makes the section into a paragraph. For example, in some writing styles, particularly the journalistic, a paragraph can be a single sentence. As long as the sentence expresses the central idea of the dissertation, it can function as a paragraph. Ultimately, strong paragraphs contain a sentence or unified sentences around a central idea. When the paragraph is completed, it should lead the reader through the dissertation and guide him to the understanding of what he is reading. If the paragraph is completed in a sentence or twenty, the final result will still be a paragraph.
