This situation occurred in a game I played recently, and should be pretty easy. Please let me know if I've messed anything up!
(;
;AW[ro][so][pp][qp][nq][oq][pr][os]
AB[rp][sp][pq][qq][qr][rr][qs]
C[Best play for White?]
PL[W]
(;W[sr];B[ss]
(;W[rs]C[RIGHTIt's a ko for life. White captures first, so Black must find the first threat.])
(;W[sq];B[rq])
(;W[rq];B[sq])
(;W[ps];B[sq])
)
(;W[sq]
;B[rq]LB[sr:A][ss:B]C[Black is alive. Next, if White plays A, Black can make two eyes at B, and vice versa.])
(;W[rq]
;B[sq])
(;W[rs]
;B[ss])
(;W[ss]
;B[sr])
(;W[ps]
;B[sr])
)