What the friends suggest that that if plays against the sacrifice in the Sveshikov?

1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e5 6.Nbd5 d6 7.Bg5 a6
8.Na3 b5 9.Bxf6 gxf6 10.Nd5 f5 11.Bxb5 axb5 12.Nxb5...

Which optimum one launches for the black color? And which optimum plan?

My Fritz openings book gives 12... Ra4 as the way to go for black. Then after 13. b4 you can play 13... Rxb4 with a good advantage for black. If 13. Nbc7+ Kd7 14. O-O Rxe4 and you'll have to defend a while, but if you play it well, you'll get out alive with a piece up

In my book ECO after 14… Rxe4 15.Qh5 Ne7 16.Qf7 Kc6 17.c4 Qd7 18.Na8 Ng6 with draw Y.Grunfeld - Fleck, Lugano 1980

Another ideia is 15...Qh4 16.Qf7 Be7 17.g3 Rg4 18.Nb5 f4 19.Rad1 fxg3 20.fxg3 Rxg3 = Coco - L.Pantaleoni, 1983.

12...Ra4 13.Nbc7+ Kd7 14.0-0 Rxe4 15.Qh5 Ne7 16.Qxf7 Kc6 17.c4 Rg4!? 18.Ne6 Bxe6 19.Qxe6 Rhg8 20.g3 f4!? (unclear)
if 18.h3 Rg6 (Black is Better)

This line is the same branch of the Grunfeld - Fleck, Lugano 1980 game as given in NCO except insted of 17...Qd7, 17...Rg4!?

Interesting Graw81...

I placed pro Fritz to analyze the 17… Rg4 and has given a small advantage for black color. I looked for left in Chess News, Chess Programs, Databases - Play Chess Online and the majority of the departures in this position is played… 17...Dd7 but 17…Rg4!? seems to be more interesting.