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Intangible Assets, Net (Tables)
3 Months Ended
Mar. 31, 2020
Intangible Assets, Net [Abstract]  
Schedule of intangible assets
   December 31,   March 31, 
   2019   2020 
Computer software at cost  $30,648   $30,142 
Accumulated amortization   (15,470)   (16,498)
   $15,178   $13,644