The answer is D. Their bickering over Jack's hesitation in hunting the pig.
At first Jack was hesitant to stab the pig, even though the boys really needed the meat. Ralph incites him to do it, and their bickering demonstrates there is tension and a conflict between their personalities. Jack still maintained some of his innocence, and the thought of killing a living creature was still too much for him. However, the shame of not being able to kill the pig was bigger than Jack's hesitation. When he finally confronts his fears, the boys become intoxicated by the blood-spilling. This also foreshadows more blood spilling later on, and not only the blood of animals.