Answer:
B. She wanted to break up with him.
Step-by-step explanation:
Henrik Ibsen's A Doll's House revolves around the family of the Helmers and especially the social dynamics of power. Focusing on the power play, Ibsen presents the role of a man and woman in the society of that time.
Mrs. Linde and Nils Krogstad are two of the characters aside from the main protagonists Nora and Torvald. They had previously been lovers until Mrs. Linde had to break up with Nils for she "had a helpless mother and two little brothers" and needed help which Nils wasn't able to provide. So, she had written a letter to him as, as she said, "it was my duty also to put an end to all that you felt for me".
Thus, the correct answer is option B.