C. Commas are used after a list, or to seperate two thoughts in one sentence.
D. They suggest expansiveness, or extending one's reach outward.
Throughout part 46, Whitman explains that a person's journey is his own, but it must extend beyond what the person currently knows. He compares needing to extend oneself to kicking them out of the comfort or their house or sending them off the plank into the water to swim. He introduces this idea of extending one's reach when he says "we but level that lift to pass and continue beyond."
<span>A. A paper mill eventually opened in Spain and, the art of making paper spread from here.</span>