After thoroughly reading a topic, when I know I almost understand this, I stutter in giving Viva in front of my teachers! It's not that they ask too hard questions problem is either I can not get what answer they want or they can not understand what I try to say! Sometimes they ask so easy questions that even that question seems to me a nightmare for me to answer! Last time I asked to say(In the statistical mechanics viva) 'What is system?' and I remained silent again( on optics viva) I was asked 'What is order no.(of a diffraction/interference pattern)?' again I stumbled. May be that I get good marks but in written exams but a bad viva-voice just spoils the happiness of my life! What should I do??