Because people couldn’t spell or pronounce it :)
It represents the moral and social decay that results from the uninhibited pursuit of wealth, as the rich indulge themselves with regard for nothing but their own pleasure. The valley of ashes also symbolizes the plight of the poor, like George Wilson, who live among the dirty ashes and lose their vitality as a result.
B. It establishes a slow buildup to the climax of the story.
The short sentences increase the tension of this particular “scene” in the story. They show how the narrator (the person speaking) is having to make quick decisions in order to seem innocent. The short sentences show this and increase the tension towards the climax.
I'd go with B, Meager. I hope this helps!