Correct Option (D)
The passage details Cynthia's initial state of shyness, fear, and self-doubt, contrasting it with her subsequent excellent performance during the audition. The "transformation" refers to this fundamental shift from her perceived limitations and apprehension to a confident and captivating delivery that stunned her audience. Her stunning performance is the tangible manifestation of this change.
Incorrect Options:
Cynthia's nervousness is described as her initial emotional state before and at the beginning of the audition. The transformation signifies the overcoming of this nervousness, not the nervousness itself.
The eruption of thunderous applause from the room was a direct reaction to Cynthia's excellent performance. It represents a consequence or an effect of the transformation, rather than the transformation itself.
The surprise on the faces of her classmates was a response to Cynthia's unexpected and impressive display. This reaction is an outcome of the transformation, not the transformation itself.