B. It establishes a slow buildup to the climax of the story.
The short sentences increase the tension of this particular “scene” in the story. They show how the narrator (the person speaking) is having to make quick decisions in order to seem innocent. The short sentences show this and increase the tension towards the climax.
The climax of a story is what the story revolves around, or the problem the character(s) is facing.
A moral dilemma is where you have to choose between two things, and you have a moral reason for both choices, but cannot decide which to choose from.
