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(That's right, celebrities singing the alphabet song).
Now...
Let's say we have two first graders, Steven Smith and Susan Smith.
You are the teacher of a bunch of first graders, including young Steven and Susan. So, since you want some kind of order in your classroom, you decide to have them sit alphabetically. Thus, little Steven comes before Susan. Which is probably for the best, because otherwise Steven could pull Susan's pigtails and no one really wants that.
With me so far? Good.
So now let's take this lesson and apply it to filing away folders alphabetically. You know, to keep order. STEVEN STILL COMES BEFORE SUSAN. I promise. The standard English alphabet used in the United States doesn't change from the classroom to the filing cabinet. Cross my heart. :D