The correct answer and the line in the mentioned excerpt from Henrik Ibsen's play A Doll's House that reflects the idea of obedience and control is "A songbird must have a clean beak to chirp with--no false notes!"
While the idea of control is conveyed in the entire part of Helmer, it is that sentence which best reflects it. First, he builds the tension shaking his finger at Nora when he realises she has "lied" to him and tells her that she must not do that again. Even when he grabs her by the waist he is physically showing his dominance. But the sentence "A songbird must clean beak to chirp with--no false notes!" states his control and orders obedience, with the exclamation mark and comparing her to a songbird, not even a person, and that must "chirp" whenever he wants and the "notes" or words that he wants.
The sentence shows paternalistic control, which Nora seems to confuse with love and marriage.