I'm going through some lecture notes, Fundamentals of Mathematica Programming (see the .nb file there). I'd like to be able to do the exercises right there in the notebook; but for some reason I can't figure out how to make the default cell an Input cell. In other words, when I'm clicking in that notebook to create a new cell--in the exercises--the cell is by default a text cell. I'd like for it to be an Input cell so that I don't have to manually change it each time. Ideas?