The event that can be described as part of the exposition in The Jungle Book is:
"Ten or eleven years have gone by, and Mowgli has had a wonderful life in the jungle."
This statement introduces the reader to Mowgli's background, setting the stage for who he is and the life he has led in the jungle, which is essential for understanding the context of the story. The exposition typically provides information about characters, settings, and initial circumstances, setting up the narrative for the events that follow.