Option "C" is the correct answer: Frankenstein's creation of a monster.
Considering that Gothic novels focus on the mysterious and supernatural powers, the creation of a monster by gathering body parts portrays elements of the gothic genre. Besides, the dark and gloomy settings where the story takes place as well as the macabre scientific experiment enhance feelings of horror and mystery. By doing so, Shelly makes use of the supernatural elements which are typical included in a Gothic piece of literature.