Active reading, from my understanding, is finding ways to get involved in what you are reading. An example of how to do this was to pretend like you have an intrest, or something vested in the subject. The only way I know how to define critical reading would be to repeat the definition I gave on active reading. These two styles, critical and active reading, tell people how to learn and study. A reader is more likley to remember information when using active reading tips.
Passive reading has no relation to learning or storing something for memory.
Passive reading would apply more to reading for leisure, not for an exam or class.