Correct option is A
In CPD, even with adequate contractions and cervical dilatation, the fetal head does not descend into the pelvis. This non-descent with dilatation is the clearest indicator of obstruction.
Explanation of options: (a) ✔ Correct; dilatation without descent is a classic sign of obstructed labor due to CPD. (b) ✘ Meconium-stained liquor shows fetal distress but does not confirm pelvic obstruction. (c) ✘ Breech is a malpresentation, but not diagnostic of CPD; breech can occur even with normal pelvis. (d) ✘ Effaced cervix indicates progress of labor but tells nothing about head descent or obstruction.