What did holden write composition about in The Catcher the Rye?

In The Catcher in the Rye, Holden Caulfield writes a composition about his little brother, Allie. Holden's brother died of leukemia the previous Christmas, and Holden is still grieving his death. He writes about how much he misses Allie and how he always loved spending time with him. He also writes about how Allie was different from other kids, and how he was more intelligent and sensitive. Holden concludes his composition by saying that he would rather have Allie back than anything in the world.