Final answer:
The quotation that reflects Mathilde's attitude change towards the necklace is when she expresses her ambition to be successful and do serious work in Paris.
Step-by-step explanation:
The quotation that best reflects Mathilde's attitude change towards the necklace is: 'I could do some serious work in Paris,' she said half aloud to herself. 'I suppose if I really wanted to, I could be very successful along this line.'
This quotation shows that Mathilde, who initially viewed the necklace as a burden and a symbol of her lower status, now sees it as an opportunity for success and a way to improve her life. She has become more ambitious and determined to achieve success, which indicates a significant change in her attitude towards the necklace.