Please find the best result for Black!
(japanese rules)
(;SZ[4]AW[ba]AW[da]AW[bb]AW[cd]AW[dd]AB[ab]AB[ac]AB[bd]C[Black to play. What is the best he can do?]GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]RU[Japanese]KM[0.00]PW[WeiÃx]PB[Schwarz]
(;B[bc]
(;W[cb]C[CHOICE];B[cc];W[dc];B[db];W[dc]C[Seki. Black wins by two points, 3 prisoners against 1.RIGHT])
(;W[db];B[cc];W[dc];B[cb]C[White is lostRIGHT])
(;W[dc];B[cb]C[White is deadRIGHT])
(;W[cc];B[cb]C[White is deadRIGHT]))
(;B[cc]
(;W[bc]C[CHOICE]
(;B[dc];W[cd];B[dd];W[cb]C[White wins.])
(;B[cb];W[ad]C[]
(;B[dc];W[bd])
(;B[ca];W[aa])
(;B[db];W[ca];B[bd];W[dc])))
(;W[cb]C[This gives Black a chance to reach the solution];B[bc];W[dc];B[db];W[dc]C[Black wins by two points, but White C3 was clearly a mistake.])))