What I did was to create a vector
of the same size of N, but varying from 0 to 1. I don't know if this is the best approach, but it helped me to plot the curves. The problem is I thought I had to chose only one correct answer, so I could not choose c or d, because for me they were both correct for large N.
I don't know if this will work, but here's a link to the figure.
https://docs.google.com/open?id=0By0...FRkclhvRnZMd2s