(;
GM[1]
SZ[19]
AW[dd][jd][nc][po][dp]
AB[pd][pf][pk][pq][jp]
LB[po:1]
C[Problem 11. Black to play.  

White has played in the middle of Black's moyo with an approach move at 1. How should Black respond ? ]
(;B[np]
TR[pk]

TE[2]
C[Correct Answer.  

Black should take the territory at the bottom with the knight's move of 1. This move, in combination with the marked stone, strongly attacks the solitary white stone on the lower right side. <= ]
)
(;B[oo]
LB[qp:B][qo:A]
C[Failure.  

There is a proverb which advises, 'Don't attach against a weak stone.' Black 1 violates this proverb.  

As you will later see, Black A and Black B are also bad. ]
;W[on];B[op];W[pm]
C[Now the white stones, which were previously weak, become strong and Black has no good way to attack them. <= ]
)
)