In a class of one's own means much better than others of the same type. The correct answer is this meaning because the expression is used figuratively, not only by its literal words.

Examples:

• As a debater, she is in a class of her own.
• In an HSC essay, In a class of one's own can express this meaning: much better than others of the same type.
• When this expression appears in a passage, connect In a class of one's own with the idea of much better than others of the same type.