It isn't the setting. From this quotation, we hardly know where we are other than listening to two employees talking about their boss.
It isn't creating humor. A Christmas Carol contains very little humor, and that which it does is mostly in the Alistair Sim movie at the end. I think you can find that on U tube and if you can, be sure and watch it. You can't study Scrooge and not know about the 1951 production.
One of your choices has to be about theme. This is the story of redemention of what was a very fine young man to a crotchety somewhat ugly old man. But the spirits saw something in him and decided to revamp that good young man.
Having said that, I think you are developing tone or dealing with characterization. It's very hard to pick. Those two are so intertwined you don't know which one to pick.
Answer
Building Theme. Scrooge is almost entirely about theme.
Developing Character: Scrooge, by the end of this is saying that he would like to have a word with his Clerk. He's learned something!!!
Note
Don't be surprised if it is tone. There is plenty of that going on in a Christmas Carol as well. The point though is that we are looking at the Transformation of Scrooge.
