The statement that best describes the conflict is: Nora has forged her father's name on the loan she received from Krogstad, and he is threatening to expose her to Helmer.
That is precisely the main plot of the play <em>A Doll's House</em>: Nora borrowed some money from the bank after forging her father's signature. She used the money to take her husband, Torvald, to Italy where he would recover from a disease. Torvald works at the bank where Nora got the loan and he is now about to fire an employee, Krogstad. That is why Krogstad decides to blackmail Nora. He tells her that, if she doesn't convince her husband to not fire him, he will reveal the truth about the loan.
