Completed exercise and added questions into intro file.

Again -- it's easy to experiment and figure it out yourself. Try taking it out, or adding two of them, and see what happens.

You can see the pattern I'm proposing here -- a quick experiment, supplemented by skimming the relevant docs, will be far faster than asking somebody a question about it.  Even if you still have to ask a question after doing some quick research, the act of having done it will make your question far more informed and clear than if you hadn't.