A quantum leap means a very large and sudden improvement or change. The correct answer is this meaning because the expression is used figuratively, not only by its literal words.

Examples:

• The new lab created a quantum leap in science education.
• In an HSC essay, A quantum leap can express this meaning: a very large and sudden improvement or change.
• When this expression appears in a passage, connect A quantum leap with the idea of a very large and sudden improvement or change.