Final answer:
The correct answer is 3) Metaphor. The teacher is using metaphor as a vocabulary application to describe unwanted noise in their class.
Step-by-step explanation:
The teacher is using metaphor as a vocabulary application when they say, "Don't bring that cacophony into my class." A metaphor is a figure of speech that directly compares two unlike things without using "like" or "as". In this case, the teacher is metaphorically comparing the unwanted noise in their class to a cacophony, which means a harsh, unpleasant mixture of sounds. A metaphor is a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable. Therefore, the correct answer would be 3) Metaphor.