In the story, Nuttel is given letters of introduction by his sister. What's the purpose of these letters? A. to attend a particular social event
B. to apply for a job
c. to ask for a hand in marriage
D. to make social calls

D. To make social calls.

Explanation:

The short story "The Open Window" by Saki a.k.a. H. H. Munro is about the main character Framton Nuttel and his retreat to the countryside. The story is a hilarious yet horrific experience for Nuttel who became the latest victim of the playful niece, Vera's love of storytelling.

Framton Nuttel has been advised by his doctor to not exert himself mentally. In a bid to cure his nervous condition, he had gone to the countryside to relax and calm himself. And to make himself acquainted with the neighbors of that retreat, his sister had written letters of introduction to help him in his social calls.

Thus, the correct answer is option D.