(;CA[gb2312]AB[sr][sp][sq][rp][qp][pp][op][np][mp][lq][lr][ls][qr][pr]AW[mr][ms]
[or][pq][qq][rq][rr][oq][qs]C[Black first to kill
]AP[MultiGo:4.4.4]SZ[19]AB[rs]
MULTIGOGM[1]

(;B[ps];W[os]C[If black captures first, white makes two eyes])
(;B[nq];W[nr]C[Black 1 doesn't help, so it seems that white 2 is a pretty important point])
(;B[nr];W[nq]C[Answer\:
Black 1, white has to respond.];B[mq];W[ns];B[ps]C[By exchanging 1-4, black successfully wasted white's liberty, Thus white cannot go P1.]
;W[os];B[nr]))