I think it's C) "It creates tension by moving fron the slower pace of the description to the faster pace of Bob's dialogue, which suggests an uneasiness on Bob's part."
Because even though I only read this part of the passage just now, instead of the full story, I can tell the description of either character, wasn't too detailed. Not to mention the pacing did start out normally, but it felt as though Bob chimed in a little too quickly.
I hope this answer satisfies you. Also please let me know if it's right or not :)
