D. an informative speech
If you wanted to give a speech to teach an audience how to start a garden, the type of speech you would want to give would be an informative speech. An entertaining speech would only entertain. A persuasive speech would be argumentative and try to convince (not teach) your audience to see your point of view. An extemporaneous speech is a speech that you would make up on the spot and not something you would want to do if trying to teach because “winging it” would not be recommended. If you are trying to assist or instruct your audience and otherwise inform them on the specificities and steps of starting a garden, again, you would want to give an informative speech.