The third most popular move, simply ignoring 6...Bf5.
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. g1f3  3... d7d5  4. c4d5 The first important moment. Nepomniachtchi has been confidently playing the line with 4. Nc3 c5, which sometimes leads to long forced draws. This system was played by So in this round. Instead of getting into a theoretical battle, Carlsen tries to take the game into his own turf. 4... e6d5  5. b1c3  5... c7c6 The problem for White in this line is that there is no way to prevent the black bishop from developing to f5. Usually in the Queen's Gambit exchange variation it's possible to avoid this by placing a bishop on d3 or the queen on c2. In this game's move order, Black can force the development of the bishop, even if he has to play g6 first.