I'd say the correct answer is C. don’t be a couch potato, read at least 20 minutes a day.
A persuasive speech is there to persuade people to do something. In this case, the narrator wants to persuade kids to read more. A is incorrect because that is not persuasive; B is incorrect because it is too early for these kids to listen to such a speech; D is incorrect because again, you are not persuading them to do anything.
