The whole paragraph 13 from "I thought I'd used up all my adrenaline to answering the questions" is used to ______.
A．describe the writer's reflection of what he should have done before the exam
B．describe the depressed feeling of the writer when knowing he failed in the exam
C．describe worrying mood in the exam and contradictory thoughts over his work at his philosophical class
D．describe how sorry the writer was feeling for his not having been working enough for his philosophical class