Answer:
A. Nicki is a round character; Nicki's father is a flat character.
Step-by-step explanation:
The terms flat character and round character were coined by Edward Morgan Forster and first mentioned in his book Aspects of the Novel (1927). These two types refer to the kind of development characters go through from the beginning to the end of a literary work.
Flat characters do not change throughout the story. They are relatively uncomplicated, especially compared with round characters, who go through sometimes drastic change. In the given excerpt, we have a contrast between Nicki, who has grown and changed, and her father, who stayed the same as before.