Answer:
The dramatic irony is used by Ibsen in the following manner:
A. Mrs. Linde knows that she has always loved Krogstad, and so does the audience, but Krogstad does not know this at the beginning of the scene.
Step-by-step explanation:
Krogstad and Mrs. Linde are characters in the play "A Doll's House", by Henrik Ibsen. As we can see in this excerpt, Mrs. Linde and Krogstad were in love once. She, however, broke up with him in order to marry a rich man. She did not do it because she did not love Krogstad. It was only because she had to think of her family and their well being. Still, when she wrote him the letter that would end their relationship, she made it seem as if she had no feelings left for him. Krogstad was deeply hurt and, as is made clear in their dialog, is still resentful over that. What he does not know is that she only made it seem that her feelings were gone because she thought it would be better that way. She has always loved him, and the audience knows that - it is Krogstad himself who does not know it. That constitutes dramatic irony - the audience knows something that the character does not.