At a pinch means if necessary, especially in a difficult situation. The correct answer is this meaning because the expression is used figuratively, not only by its literal words.

Examples:

• At a pinch, the small room can hold fifty students.
• In an HSC essay, At a pinch can express this meaning: if necessary, especially in a difficult situation.
• When this expression appears in a passage, connect At a pinch with the idea of if necessary, especially in a difficult situation.