Note the position by 30. Nf4. Carlsen has piled up both rooks on the c-file targeting the c7 pawn; and his Queen and Knight are targeting the d5 pawn. Black is so tied up to the defense of these two weak pawns, that White is given options for other plans, such as maneuvering his remaining knight to the c3 square bringing one more piece against the d5 pawn. Or pawn storming Black's castled King.

A backward pawn on c7? Doubled rooks on the c file? Indeed, a game of Botvinnik. > Lilienthal vs Botvinnik, 1940

14 a3 gets ready for the famous minority attack b4. Black cannot just sit and do nothing. If Black does not make good use of his time White will gain the advantage, as he does.

Four alternatives for Black seen in the past are (1) To try a king side minority attack by ...f5 as in the game Botvinnik vs Bronstein, 1951 (2) To try a king attack with the pieces as in the game G Andruet vs Spassky, 1988 (3) To play ...b5 and play his own knight to c4 whilst White plays a N to c5 as in the game Benko vs Petrosian, 1963 and (4) To allow the White to play the minority attack b5, and to exchange the b5 pawn for Black's c6 pawn but then to transform Black's b pawn from a target into a weapon as in the game Spassky vs Petrosian, 1969

One question then is this: Which of these four courses is the most advisable for Black?

4...Bb4 also missing it (4...dxc4!)

5.cxd5 white realizes the pawn could have been won so is quick to swap it off

6.Bg5 after this move both clergymen threaten to steal a horse

8.Qa4+ White thinks he's won a piece (the unprotected bishop at b4) but he missed black's next move

8...Nc6!! blocking the check and protecting the bishop

12...Bd6 black decides he's not in the mood for horse tonight

13.Qd1 white's queen returns home without having won the piece

16.Na4 white plans to stick his knight on the c5 outpost, hoping black will miss this

16...b6! black is no fish, he prevents this

17.Nb2 horse returns to the stable

33.Nxd5! White correctly counts that there was only one defender defending whereas there were two attackers attacking so he captures

Takes cxd5 to gain the half open c file to play for pressure along this file and start a minority attack.

Basically a QGD with White getting the problem queen bishop out of the way of q-side play. White plays the q-bishop out and then builds his dark squared pawn chain.

Rotate a knight towards c5 as a threat to cause Black to further weaken his q-side pawns.

Then rotate pieces back to the k-side while still maintaining pressure on c7.

When White plays like this it's hard sometimes to suggest what Black should do to respond. Perhaps play to exchange pieces, especially queens.