The Crossing of Internal and External Diegetic Sound Borders in the Snake

The crossing of internal and external diegetic sound borders in The Snake Pit accomplishes what narrative goal?

A) It gives the viewer a better sense of the spatial dimensions of the mise-en-scene.
B) It gives the viewer access to the larger political context of the story.
C) It confuses the viewer in order to then reveal the protagonist's state of mind.
D) It provides the viewer with an intimate understanding of the protagonist's sexuality.