35.1

The position in the diagram is typical. Such a pawn structure arises in many systems. Black's plan is the f7-f5 advance. After the exchange on f5 (otherwise the attack f5-f4, g6-g5-g4), the two black pawns are ready to drive back the white pieces and revive the g7 bishop. And the king will go to h8, under the cover of the h7 pawn, freeing the "g"-file. Botvinnik's idea is to remove the cover by h2-h4-h5-hxg6, after which the f7-f5 advance is very risky. Besides, White get the g5 square.