Mrs. Loisel borrowed the necklace from Madame Forestier.

Explanation:
Madame Forestier:
- Madame Forestier is a wealthy friend of Mrs. Loisel.
- She is described as having a rich and luxurious lifestyle.
- She owns many expensive and beautiful jewels, including the necklace that Mrs. Loisel borrows.

The Necklace:
- The necklace is a stunning piece of jewelry that Mrs. Loisel covets.
- It is made of diamonds and is very expensive.
- Mrs. Loisel's desire to wear such jewelry is one of the main reasons she borrows the necklace.

The Borrowing:
- Mrs. Loisel borrows the necklace from Madame Forestier to wear to a high-profile event.
- She believes that wearing such an exquisite necklace will enhance her beauty and make her more confident.
- Madame Forestier agrees to lend the necklace, considering her friendship with Mrs. Loisel.

The Loss:
- Unfortunately, Mrs. Loisel loses the necklace while she is at the event.
- She and her husband search frantically for it but are unable to find it.
- Fearing Madame Forestier's reaction, they decide to replace it without her knowledge.

The Debt:
- Mrs. Loisel and her husband purchase a new necklace to replace the lost one.
- They spend a large sum of money and go into debt to afford the new necklace.
- They do not disclose the truth to Madame Forestier and hope she will not notice the substitution.

The Revelation:
- After years of hard work and sacrifice to repay their debts, Mrs. Loisel finally reveals the truth to Madame Forestier.
- She confesses that she lost her necklace and replaced it with a new one.
- To her surprise, Madame Forestier tells Mrs. Loisel that the original necklace was a fake and worth much less than she had believed.

The Lesson:
- The story of Mrs. Loisel borrowing the necklace and going into debt symbolizes the theme of appearances and social status.
- It teaches the importance of being honest and content with one's own circumstances instead of constantly striving for material possessions and societal validation.

Answer is B