CHESSDORRAPawn promotion
Four choices on the last rank.
The four choices
A pawn that reaches the farthest rank immediately promotes to a queen, rook, bishop, or knight of its own colour. You can choose a piece even if you already have one on the board.
When a knight is needed
A knight attacks squares a queen on the same square does not. Compare all four promotions: one may give the required check while another allows a defense or even causes stalemate.