Black to play - How can black kill the white stones
(;AB[qa]AB[qb]AB[qc]AB[pc]AB[oc]AB[nd]AB[md]AB[lc]AB[kc]AB[jc]AB[jb]AB[ja]AW[ka]AW[kb]AW[lb]AW[mb]AW[mc]AW[ma]AW[nc]AW[ob]AW[pb]C[If White plays now, he can guarantee himself 2 eyes.]AP[goproblems]
(;B[oa]C[Now white cannot make two eyes and is dead.RIGHT])
(;B[pa]C[Now white cannot make two eyes and is dead. If black were to have played at Q19 then white would play at P19 and will be able to make 2 eyes, using 2 different locations.CHOICE];W[oa]C[Now white cannot make 2 eyes and is dead.]))