Answer:
D. Matilda's desire to be "better" than she is, and part of a higher class.
Step-by-step explanation:
The fact that Matilda was born in a class below her beauty is not necessarily a problem, as many people would be able to be happy under these conditions. However, the real problem is the fact that Matilda wants to be part of a higher, richer class. This causes dissatisfaction within herself. The situation is the one that sets the events of the plot in motion, as it is the reason why Matilda decides to borrow the fancy necklace.