"Two, because the evidence of mastery is the ability to explain, not simply to perform."

So true. I learn more by writing about things than by reading about them (of course, the former includes a lot of the latter, but it's so much more productive when you're reading towards a specific goal...and if the goal is explaining the subject clearly and entertainingly you really have to have a firm grasp of the subject). It just seems to activate my brain in ways that merely reading never quite does. Doing the exercises overcomes the passivity of reading to some degree, but writing down what you learned takes it up another notch.