Explanation:

- The sentence describes "unruly behaviour," which generally has a negative connotation.

- Comforted: This means to soothe or bring relief. Unruly behavior typically wouldn't bring comfort to a teacher, especially if they are trying to maintain order in the classroom.

- Irritated: To irritate means to cause annoyance or displeasure. Unruly behavior is very likely to cause irritation to a teacher trying to control a classroom.

- This is the most appropriate word to fill the blank.

- Calmed: To calm means to soothe or bring peace. The nature of "unruly behaviour" is disruptive, so it does not fit the meaning of calming someone.

- Pleased: This means to bring happiness or satisfaction. It is unlikely that a teacher would be pleased by unruly behavior, which usually disrupts teaching.