When mr. darcy is writing a letter early in the novel, miss bingley gives him constant attention, commenting "on his handwriting, or on the evenness of his line, or on the length of his letter " why does austen includes these details?

There exists the same question that has the following choices

A. She is showing how rude Mr.Darcy is response
B. She is comparing Miss Blingly and Mrs.Hurst
C. She is making fun of Miss Blingy for the false interest
D. She wants readers to know the importance of letters at the time

The correct answer is letter D. She wants readers to know the importance of letters at the time.