Light and darkness are two opposite things being contradicted in this sentence; this is antithesis.
Greg shows himself to be a dynamic character because he changes over the course of the story and learns a valuable lesson. He learns not to make assumptions about people based on the way they look. Lemon Brown shows Greg that he is a caring and brave person who lost his son in a war. This changes how Greg thinks about his own father.
The element necessary to complete the sentence above is D) independent clause.
You already have a subject (I) and a predicate (save), so these two are not needed, nor is a prepositional phrase. But you need an independent clause, because this is a dependent clause which cannot stand on its own. For example:
If I save enough money, <em>I will buy a car. </em>
