Case issues

[lynxypoo.livejournal.com]

Does anyone know where I might find something to practice recognizing differences in the nomnative, prepositional, and accusative case? (I'll be learning the instrumental case in the next chapter).

behind the cut are a coulple excerpts from my latest excercise, what I thought it was, and what it should be- I just ask why?
( why? )

спасибо!