Part A: The best conclusion drawn by the Chorus after the Oedipus-Teiresias episode is: C. Oedipus will no longer be able to save the city even though he was able to save it from the Sphinx.
Part B: The line from the antistrophes that best supports the answer to Part A is: D. Chorus. …He saved our city from the Sphinx / Was tested hard and shone like gold. / to my mind he is wise and guilt-free.
This line highlights the contrast between Oedipus's past success in saving Thebes from the Sphinx and the current situation where his ability to help is in doubt.