In general, it is "D. all of these" that should be considered when trying to discover the theme of a piece of literature, since pretty much any element can develop a theme.
Answer:
The slenderman myth scared many children and has been a facinating story to kids and adults alike for years.
The Pony Express linked east and west, being the first rapid transit and the first mail line in the entire continent. It also marked the highest development of land travel before the arrival of the Pacific Railroad. It was an achievement of physical resistance of man and horse.
