The answer would be letter C. It introduces the narrator and the situation.
In the short story Whistling My Worries Away, the narrator, Benito, offers some backstory to explain why he is taking the bus at the crack of dawn to spend the day with a bunch of seven-year-olds.
This backstory is a device called exposition in literature. It gives the reader the information needed to better understand the characters and the plot. In this short story, the exposition lets us know that Benito was convinced to take a summer job at a kids camp by his cousin. Even though he has experience with plays, he has never worked with children before and is now supposed to help them come up with a skit. Benito decides to take the offer not only to help his cousin, but also to save some money and buy a new computer.
Note: you didn't include the passage, so I assumed it is the beginning of the story.