A very very easy problem :)
Please find the best result for Black!
(japanese rules)
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[4]KM[0.00]
PW[Weiß]PB[Schwarz]AW[ca][bb]AB[cb][ac][ad]C[Black to play - what's the best he can do?]
(;B[cc]CR[cc]
;W[bc]CR[bc]
;B[bd]CR[bd]
;W[cd]CR[cd]
;B[dd]CR[dd]
;W[ab]CR[ab]
(;B[ba]CR[ba]
;W[cd]CR[cd]
(;B[bd]CR[bd]C[...and Black wins! RIGHT])
(;B[da]CR[da]
;W[dc]CR[dc]C[White wins]))
(;B[cd]CR[cd]
;W[db]CR[db]C[White wins]))
(;B[bc]CR[bc]
;W[cc]CR[cc]C[White wins]))