At one's peril means with serious risk to oneself. The correct answer is this meaning because the expression is used figuratively, not only by its literal words.

Examples:

• Ignore the warning at your peril.
• In an HSC essay, At one's peril can express this meaning: with serious risk to oneself.
• When this expression appears in a passage, connect At one's peril with the idea of with serious risk to oneself.