Will anybody help me by telling me the strategy to the Europe Challenge and Crazy Challenge?

EU challenge- you try to break the bonuses as quickly as possible, but just protecting your core bonuses (UK), your opponent will have some large stacks, use the airlifts. Quite easy for me.

Crazy challenge- I used to struggle with this too. But then after playinng multiplayer, Strat 1v1 games, winning was a breeze for me. Its important you get a nice start, starting in a 3 or 4 bonus and not surronded from all sides. My advice for this level is: practice more on multiplayer, then get back to the crazy challenge.

In Europe: Take Norway/Sweden from your "Ally".
Push hard with your reserves into the center.
Send all airlifts to your Ally, next to the enemy's stack.(check where he's deploying, send it there.)

Deploy at least 1 army to every territory that borders the enemy. (Capitalize on the way the AI fights)