12 positions in rook endgames! You must know them! With explanations.

Hello! Somewhere I've started to show you endgames. And today I'm going to show you 12 positions that everyone musts know. Usually rook endgmes will end with a draw, even one of opponent has 1 or even 2 excess pawns. 

Let's start!

We must think before we move pawn on a7. And it's finish. Goodbye!