5 pts to anyone who can answer the last question here

The other day this position (or one similar to it) came up. Both are good players, but showed they still need to learn a few things. It is Black's turn. What should Black play?
a) a2  b) Rb2  c) Rd2  d)Rg2  e) e3
In the game, Black played a2, how should White have replied?

1. Black should play Rg2 threatening Rg1 pinning the rook and queening the pawn. when you're trying to queen a pawn, remember that the square(s) the pawn guards are as important as the queening square. Put a piece, especially a rook, on that square (g1) and the pawn can almost always queen.
2. a2 is a mistake because it traps the white King. It's almost stalemate - except for the rook. This leads to a situation known as the "raging rook". White will check the black king relentlessly from close range and the rook cannot be taken lest the game end in stalemate. 1. Rd6+ Kb5 2. Rd5+ Kc4 3. Rd4+ Kc3 4. Rd3+ Kc2! 5. Rc3+ Is there any way the king can escape? If yes, how? If no, how must white play. Although in some positions the king can escape, many times he cannot and the game ends in a draw. So be very careful not to "stalemate" your opponent's king thinking he can still move his rook!