We have been given a proof about how angles PCQ and ABC are complimentary. There we need to find the correct missing step.
If you look carefully at the proof in place of [Missing Step], then you will notice that we have to give reason about how angles OCP and ABC are equal.
Only choice which is talking about angles OCP and ABC is 4th choice.
Which shows that OCP and ABC are corresponding angles.
Hence 4th choice "For parallel lines cut by a transversal, corresponding angles are congruent, so ∠OCP ≅ ∠ABC.