I'd elaborate on the source, but I can't read Chinese.
(;AW[jq]AB[op]AB[qp]AB[cp]AB[eq]LB[hq:A]LB[lq:B]C[A or B?FORCE]AP[goproblems]
(;B[lq];W[gq]C[Yup! Good shape and protects from white slipping underneath the 4th lines stones.RIGHT])
(;B[hq];W[mq]C[Black is open in this corner now.]))