C. The rest are letters to people in familiar situations.
To persuade the reader in such a way, they want to take action towards something.
Usually, in a conclusion, you wrap up what you have been writing about the whole time. So, a conclusion is basically a summary of the whole text. You can introduce new ideas for the reader, but it is usually inadvisable. In a couple of sentences, you should finish your text, referring to the previous paragraphs and just wrap it all up nicely.
