Read the excerpt from "homesickness."

only a month before, my ancient half-sister, who was twelve years older than me, had actually had appendicitis, and for several days before her operation i was able to observe her behavior at close quarters. i noticed that the thing she complained about most was a severe pain down in the lower right side of her tummy. as well as this, she kept being sick and refused to eat and ran a temperature.

why does the author include information about the narrator's sister?

to show how the narrator gets the idea for his trick
to demonstrate that the narrator is immature
to demonstrate that the narrator is insensitive
to show why the narrator misses his family