once when i was asked this by my boss i replied 'fine thankyou', my boss then came back with 'just fine?' the next time she asked i replied with 'ok thankyou' it seems 'ok' is not good enough either, so the next day i replied 'couldn't be better thankyou!' and was met with good! so it seems that if asked how you are the reply is 'couldn't be better'
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