To control a 4*4 chessboard, you must put at least two queens. First of all, the first queen is of course any one of the 2*2 squares placed in the middle, which can play the greatest role, but according to its walking method, the horse can't walk, so four Japanese squares in the sixteen squares can't be controlled, so the second queen should be placed in two squares (one corner of sixteen squares) diagonally opposite to the first queen, so that all sixteen squares can be controlled.

Finally, it is concluded that only a 4x4 chessboard can be controlled when two queens are placed on the two corners of the oblique angle of a nine-square grid.

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