Punctuate the paragraph please.?

the central thought, or main controlling idea of a paragraph, is usually conveyed in what is called a topic sentence. this crucial sentence, which states, summarises, or clearly expresses the main theme, is the keystone of a well-built paragraph. the topic sentence may come anywhere in the paragraph, though most logically and in most cases it is the first sentence. this immediately tells readers what is coming and leaves them in no doubt about the overall controlling idea. in a very long paragraph, the initial topic sentence may even be restated or given a more significant emphasis in its conclusion.