This is an example of foreshadowing. This is when the plot gives you details, so in this case the nightmare, that symbolizes a dreadful event will take place sometime later in the story. Foreshadowing is a technique used to hint at something that will transpire in the story and the foreshadowing nearly always appears at the beginning of the story.
D, with the most simple. When writing speeches/voicing speeches, always go from simple to complex so your listeners or readers can follow the point you are trying to get across.
