The correct answer is: A. brought about disharmony.
A rift in the lute is a metaphor for disharmony or discord. In this case, the arrival of the mother-in-law has caused disharmony in the family. This is because the mother-in-law is a new person in the family, and she may have different ideas about how things should be done. This can lead to conflict and disagreements between the mother-in-law and the other members of the family.
The other options are incorrect because they do not accurately describe the situation. Option B is incorrect because the arrival of the mother-in-law does not necessarily bring about a disciplined atmosphere. Option C is incorrect because the arrival of the mother-in-law does not necessarily cause unnecessary worry. Option D is incorrect because the arrival of the mother-in-law does not necessarily cause a pleasant atmosphere.
In conclusion, the correct answer is: A. brought about disharmony.