A last-ditch effort means a final desperate attempt to solve a problem or avoid failure. The correct answer is this meaning because the expression is used figuratively, not only by its literal words.

Examples:

• The doctors made a last-ditch effort to save the patient.
• In an HSC essay, A last-ditch effort can express this meaning: a final desperate attempt to solve a problem or avoid failure.
• When this expression appears in a passage, connect A last-ditch effort with the idea of a final desperate attempt to solve a problem or avoid failure.