Confidence is key – Say anything, but say it like you mean it. Professors love enthusiasm.
Answer a different question – “That’s an interesting question, but what’s even more fascinating is…” proceeds to talk about something vaguely related.
Repeat the question slowly – Buy time, sound deep. Maybe the answer will magically appear in your brain.
Throw in buzzwords – “From a socio-economic perspective… in today’s dynamic landscape…” Boom, instant credibility.
Smile and hope for mercy.
And if all else fails… fake a coughing fit.