Puzzle of the week #232

Level: 
2-Knight
Chess Diagram: 

[Event "Puzzle #232"][Date "2013.10.04"][Result "1-0"][SetUp "1"][FEN "k7/8/K2B4/8/2N5/8/8/8 w - - 0 1"]

We start a new journey with a new group of students eager to learn the game. After the previous simple puzzle (sample for the admission test) we move on to something a bit more complicated. White to move:
a) Is this position possible or impossible to reach while playing?
If you think this is a possible position:
b1) Write the last White and Black move made to reach it
b2) Show how White wins the game

Total available points for this puzzle is 15. The answers will be published next week together with puzzle #233.

Puzzle #231 solution:
Valeriu Coada #296, Chisinau 2004. Out of all Black pieces, only Be2 defends the Black King; the Knights are actually useless and in the way. White uses Bg2 to control the diagonal h1-a8, Rc1 to control the c-file and the Knight to deliver checkmate. Solution:

[Event "Puzzle #231"][Date "2013.08.18"][Result "1-0"][SetUp "1"][FEN "1kn5/n5p1/6P1/2N5/1p6/1P6/1K2b1B1/2R5 w - - 0 1"]1.Nd7#

Comment: 

Basic mates