Don't worry if they didn't ask about optional and past experience, what matters is: what they asked and how you responded. Even dropping a question is not a big deal. I remember I dropped 4, 5 questions and they asked me just 1 question from my optional, still I got 207 marks.

What I believe after my interview is that
1. One should respond normally(with a smile) when a question is dropped.
2. Be logical and never throw guesses if you don't know exact answer.
3. Saying a polite sorry is much better than giving a confused answer.
4. Never confront unnecessarily on some argument and if you are not ready to leave your stance just agree to disagree.
5. Listen the complete question, never start before interviewer has completed his question.
6. Think for a while to start your answer.
7. If you are stopped, stop immediately even if your answer is not complete.
8. Try to keep discussion in your safety zone, never coin a term that you are not familiar with.
9. Do not show contradiction in your statements, even it asked by a different panel member your previous answer and latest one should show same stance.
10. some times panel tells you exact answer if you fail to answer, say a thanks to them for this information.

These are my personal observations seniors can comment with more authenticity.

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For every minute you are angry you lose sixty seconds of happiness