EVENT
BOARDSIZE 19
SETUP W D16 G16 D4 K4 O3 M17 M15 N15 N14 
SETUP B C9 Q4 Q6 Q10 Q16 K16 L15 L14 M14 
MARK \t@N14 A@N13 B@P13 C@Q13
COM
Problem 118. Black to play.  

White has just played the marked stone in order to prevent Black
from confining her to the top. How should Black respond; at A,
B, or C ? 
ENDCOM
B 1 Q13
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should defend the right side with 1.
ENDCOM
  VAR
  B 1 P13
  COM
  Failure.

  Black 1 here would be an overplay.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 N13
  COM
  Failure.

  Black 1 aims to confine White to the top, but ...
  ENDCOM
  W 2 P15
  COM
  ... she responds with 2 ...
  ENDCOM
  B 3 Q15
    VAR
    B 3 P13
    COM
    If Black 3 here, ...
    ENDCOM
    W 4 Q15
    COM
    ... White will play 4 and Black will be unable to put his thickness
    to good use.
    <=
    ENDCOM
    ENDVAR
  W 4 O13
  COM
  ... and 4, leaving Black without a good follow-up.
  <=
  ENDCOM
  ENDVAR
W 2 N12
COM
White must escape with 2 ...
ENDCOM
B 3 L12
W 4 N10
COM
... and 4, but ...
ENDCOM
B 5 L10
MARK 3@L12
COM
... Black moves out into the center with 3 and 5, pinning the
white group against his stones on the right.
<=
ENDCOM