At a critical juncture means at an important point when a decision or change is needed. The correct answer is this meaning because the expression is used figuratively, not only by its literal words.

Examples:

• The country stood at a critical juncture after the election.
• In an HSC essay, At a critical juncture can express this meaning: at an important point when a decision or change is needed.
• When this expression appears in a passage, connect At a critical juncture with the idea of at an important point when a decision or change is needed.