RE: Can a girl and a boy be just best friends?
This is such an interesting question.
First, I love your "qualified answer" that "terms and conditions apply." That sure made me smile.
I'd like to take a run at it from my slightly different personal perspective...
I would say that the answer is definitely yes, and (expanding a bit on your Terms and Conditions) I think there is a good reason that this is a question at all.
As a Christian, I think the reason is that, in the course of a "normal lifetime," the complications of physical involvement make it very difficult to happily engage with multiple partners in all ways. The bible contemplates marriage as a life-long commitment. I think this primarily for the benefit of the children and grandchildren and so-on.
Recognizing that, I think that friendships can and should be encouraged all around. There are people of both sexes that may have similar interests to yours, and whose friendship can be very beneficial when it comes to encouraging development and creativity.
Thanks for this thought provoking article!