Answer:
The part of the plot structure that this excerpt illustrates is:
C. exposition
Step-by-step explanation:
In literature, exposition is the part of a story in which the author sets the stage for what will happen. It is where the theme, characters, conflicts, setting and/or circumstances are laid out. This is, for obvious reasons, usually placed at the very beginning of the story. The excerpt we are studying here has the opening "once upon a time," which is typical of the beginning of short stories, fables, and fairy tales. However, even if it didn't have such an opening, the excerpt is still introducing the characters and information about them, as well as the existing conflict caused by jealousy.