Explanation:

- The passage discusses a decision by the principal to take action against a student named Lin Piao due to his frequent absence from classes.

- The sentence in question is "So he sent for the (4)______ man."

- The options provided are:

- Immature: Implies a lack of maturity, often used to describe behavior, not necessarily age.

- Young: Refers to someone who is youthful, generally appropriate when describing a student.

- Youthful: Suggests appearing young, often used for appearance rather than age.

- Childish: Connotes immature behavior, typically negative, not suitable for this context.

- Given that Lin Piao is a student, the term that best fits is “young.”

Young is the most appropriate choice for blank no. 4.