user3405:  [FEN ""]
  1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nc3 exd5 5.cxd5 d6 6.e4 g6 7.f4 Bg7 8.Bb5+

How can black respond in the following position?

user2429: 8...Nfd7 is the most popular line among Grandmasters. 
Bareev vs Topalov 2002, 0-1
Bostari vs Polgar 2011 0-1
8...Nbd7 is extremely risky and requires thorough preparation. White does seem to get at least a minimal endgame advantage in the 8...Nbd7 line with best play by Black. Since the advent of strong engines, Grandmasters have avoided it and I would recommend avoiding it as well. 
8...Bd7 is just bad and White easily gets an advantage. 
I provide some sample lines - 
     [Event "8...Nfd7 is Black's best move"]
     [Date "2014.10.26"]          
     [FEN ""]

     1. d4 Nf6 2. c4 e6 3. Nc3 c5 4. d5 exd5 5. cxd5 d6 6. e4 g6 7. f4 Bg7 8. Bb5+
     Nfd7 (8... Nbd7 9. e5 dxe5 10. fxe5 Nh5 11. e6 Qh4+ 12. g3! (12. Kd2?! fxe6 13.
     dxe6 O-O 14. exd7 Bxd7 15. Bxd7 Rf2+ 16. Nge2 Rd8=) 12... Nxg3 13. hxg3 Qxh1 14.
     Be3 Bxc3+ (14... O-O 15. exd7 Bxd7 16. Bxd7 Rfe8 17. Bxe8 Rxe8 18. Qe2 Bh6 19.
     Kf1 Bxe3 20. Qg2) (14... Qg2 15. exd7+ Bxd7 16. Bxd7+ Kxd7 17. Qg4+ Kd8 18.
     O-O-O) 15. bxc3 a6 16. exd7+ Bxd7 17. Bxd7+ Kxd7 18. Qg4+ f5 19. Qf3 Qxf3 20.
     Nxf3) (8... Bd7? 9. e5 dxe5 (9... Qe7 10. Qe2 dxe5 (10... Nh5 11. g4) 11. d6)
     10. fxe5 Nh5 11. Nf3 O-O 12. Bxd7 Nxd7 13. g4) 9. a4 O-O (9... Qh4+!? 10. g3 Qe7
     11. Nf3 O-O 12. O-O Na6 13. Re1 Nb4) 10. Nf3 Na6 11. O-O Nb4 12. Re1 a6 13. Bf1
     Re8


3405: <pre><code> [FEN ""]
  1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nc3 exd5 5.cxd5 d6 6.e4 g6 7.f4 Bg7 8.Bb5+
</code></pre>

<p>How can black respond in the following position?</p>
 2429: <p><strong>8...Nfd7</strong> is the most popular line among Grandmasters. </p>

<p><a href="http://www.chessgames.com/perl/chessgame?gid=1252423">Bareev vs Topalov 2002, 0-1</a></p>

<p><a href="http://www.chessgames.com/perl/chessgame?gid=1693668">Bostari vs Polgar 2011 0-1</a></p>

<p><strong>8...Nbd7</strong> is extremely risky and requires thorough preparation. White does seem to get at least a minimal endgame advantage in the 8...Nbd7 line with best play by Black. Since the advent of strong engines, Grandmasters have avoided it and I would recommend avoiding it as well. </p>

<p><strong>8...Bd7</strong> is just bad and White easily gets an advantage. </p>

<p>I provide some sample lines - </p>

<pre><code>     [Event "8...Nfd7 is Black's best move"]
     [Date "2014.10.26"]          
     [FEN ""]

     1. d4 Nf6 2. c4 e6 3. Nc3 c5 4. d5 exd5 5. cxd5 d6 6. e4 g6 7. f4 Bg7 8. Bb5+
     Nfd7 (8... Nbd7 9. e5 dxe5 10. fxe5 Nh5 11. e6 Qh4+ 12. g3! (12. Kd2?! fxe6 13.
     dxe6 O-O 14. exd7 Bxd7 15. Bxd7 Rf2+ 16. Nge2 Rd8=) 12... Nxg3 13. hxg3 Qxh1 14.
     Be3 Bxc3+ (14... O-O 15. exd7 Bxd7 16. Bxd7 Rfe8 17. Bxe8 Rxe8 18. Qe2 Bh6 19.
     Kf1 Bxe3 20. Qg2) (14... Qg2 15. exd7+ Bxd7 16. Bxd7+ Kxd7 17. Qg4+ Kd8 18.
     O-O-O) 15. bxc3 a6 16. exd7+ Bxd7 17. Bxd7+ Kxd7 18. Qg4+ f5 19. Qf3 Qxf3 20.
     Nxf3) (8... Bd7? 9. e5 dxe5 (9... Qe7 10. Qe2 dxe5 (10... Nh5 11. g4) 11. d6)
     10. fxe5 Nh5 11. Nf3 O-O 12. Bxd7 Nxd7 13. g4) 9. a4 O-O (9... Qh4+!? 10. g3 Qe7
     11. Nf3 O-O 12. O-O Na6 13. Re1 Nb4) 10. Nf3 Na6 11. O-O Nb4 12. Re1 a6 13. Bf1
     Re8
</code></pre>
