The correct answer is "It affect the narrator's tone in a piece of writing".
Themes are underlying ideas and have nothing to do with diction and creation of precise images is managed by using vivid and descriptive writing, not with diction.
The literary device is ambiguity
From the first sight I thought that all of the options are suitable, but then I realized that the most powerful tool that makes audience to listen (not just hearing) to pay attention to the most important part of speech is to slow down or pause. It is called situational semantic pause which is used during a speech, usually after the words on which people should be focused, so that the quiet will make audience comprehend its importance.
