(;SZ[19]C[Black's response to the marked play?

Source:
    American Go Journal, Winter 1993
    "How to Choose Joseki", by Yilun Yang]TR[no]AB[qd][oc][pl][pq]AW[dd][dq][po][no];C[Hint:  A or B?]LB[nq:a][mq:b]
(;B[nq]C[The 1 space extension is a reasonable move that makes a solid shape.];W[lo];B[lq];W[pi]LB[qj:a]C[This reasonable sequence may follow.  (White could also try A here.)

Black does not have to worry about any weaknesses in his bottom formation, while later threatening White's right side stones.

])
(;B[mq]C[The 2 space extension is faster, but creates a thin shape that Black doesn't want in this position.];W[lo];B[kp];W[pi]TR[kp]C[Now, White's 3 stones in the bottom right have the extra option of exploiting Black's thinness at the bottom, if necessary.

Note though that Black's marked stone on the 4th line would look better if Black, not White, had a supporting stone near the lower left corner. ]))