The correct answer is D. There is a change in mood from the quatrains to the final couplet. This is common in the English sonnet that the final couplet is used to change the mood and add new meaning to what was previously said, thus being a sort of a peak for the sonnet.
One of the doctor's promises is that if Miss Manette tells the doctor that she feels the same as Charles, the doctor will tell her that he felt this same.
I hope this helps!
