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2. STOCK-BASED COMPENSATION - Options (Details 1) (Stock Option, USD $)
3 Months Ended
Aug. 31, 2014
Aug. 31, 2013
Stock Option
   
Expected term (in years) 4 years 4 years
Volatility 91.00% 95.00%
Expected dividend $ 0 $ 0
Risk-free interest rates 1.28% 1.46%
Estimated forfeiture rate 0.25% 0.25%
Weighted average grant date fair value $ 1.71 $ 0.92