This problem has quite a few variations, and I don't have the strength to evaluate them all. Please use the solution navigation option after the problem to see other variants, and please suggest others as you see them.
(;AB[ob]AB[nb]AB[mb]AW[ma]AW[lb]AW[mc]AW[nc]AW[oc]AB[pc]AB[pd]AB[qd]AB[re]AB[qf]AB[rg]AB[pi]AB[ph]AB[pg]AB[qj]AB[rj]AW[qi]AW[ri]AW[pj]AB[ql]AW[oj]AW[oi]AW[oh]AW[og]AW[pf]AW[pe]AW[qe]AW[oe]AW[od]C[White to play in the endgame.]AP[goproblems]
(;W[pb]
(;B[rc]C[CHOICE]
(;W[qb];B[rb]
(;W[ra]C[Good job!RIGHT])
(;W[qc];B[rd];W[oa];B[qa];W[na]C[White could get more.]))
(;W[oa];B[qb]C[White could get more.])
(;W[rb];B[qb])
(;W[na];B[qb]C[White could get more.]))
(;B[qb]C[Black fails.];W[rd];B[pa];W[qg];B[qh];W[rh];B[qg];W[sg];B[rf];W[se]C[RIGHT])
(;B[qc]C[Black should not play here...];W[rc]
(;B[rd];W[qb];B[rb];W[ra];B[sc];W[oa]C[Slightly better for white than the solution.RIGHT])
(;B[qb]
(;W[rd]
(;B[rb];W[qg];B[qh];W[rh];B[qg];W[sg];B[rf];W[se]C[RIGHT])
(;B[rh];W[rb];B[pa];W[ra]
(;B[qa];W[na]C[RIGHT])
(;B[sd];W[qa];B[pb];W[na]C[RIGHT])))
(;W[qg];B[qh];W[rh];B[qg];W[sg];B[rf];W[rd];B[si];W[rb]C[RIGHT]))))
(;W[qg];B[qh]
(;W[rh];B[qg]
(;W[sg];B[rf]
(;W[rd];B[rc]
(;W[pb]C[];B[qc]
(;W[qb];B[rb]
(;W[ra];B[pa];W[sd];B[si])
(;W[oa];B[qa];W[na]C[White can get more.]))
(;W[oa];B[qb];W[na]C[White can get more.])
(;W[rb];B[qb];W[sd];B[si]))
(;W[sd];B[sc];W[pb]C[Why waste ko threats?]))
(;W[pb]C[Why waste ko threats?]))
(;W[pb]C[Why waste the ko threats?]))
(;W[pb]C[Why waste the ko threat?])))